diff options
| author | Sebastian Trueg <trueg@kde.org> | 2009-11-30 19:16:03 +0000 |
|---|---|---|
| committer | Sebastian Trueg <trueg@kde.org> | 2009-11-30 19:16:03 +0000 |
| commit | 97ed16d3dc30e537baf7a2984c8fff3535dfc32e (patch) | |
| tree | 287d99810798324d308cec50dde553f9e98ab69c /nrl | |
| parent | 12cec34c5c50eb50fe551b725eaa36d62f3b0239 (diff) | |
Moved the docs out of the ontologies tree for two reasons: 1. we do not use them yet and 2. I will add a svn:external to kdesupport and nobody wants to download the tons of MBs that are the docs.
Diffstat (limited to 'nrl')
| -rw-r--r-- | nrl/doc/nrl-header.html | 11143 |
1 files changed, 0 insertions, 11143 deletions
diff --git a/nrl/doc/nrl-header.html b/nrl/doc/nrl-header.html deleted file mode 100644 index 6d9f543..0000000 --- a/nrl/doc/nrl-header.html +++ /dev/null @@ -1,11143 +0,0 @@ -<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> -<html style="direction: ltr;" xmlns="http://www.w3.org/1999/xhtml" lang="en-us"> -<head> - - - - - - - - <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> - - - - - - - - <link rel="stylesheet" type="text/css" href="nepomuk-ontology-docs.css" /> - - - - - - - - - - - - <title>NEPOMUK Representational Language (NRL)</title> - <meta content="Simon Scerri" name="author" /> - - - - - - - - <meta content="Specifications for the NEPOMUK Representational Language" name="description" /> -</head> - - -<body style="width: 900px; color: rgb(0, 0, 0);" alink="#ee0000" link="#0000ee" vlink="#551a8b"> - - - - -<div class="head"> -<div class="nav"> <a href="http://nepomuk.semanticdesktop.org"> </a><a href="http://nepomuk.semanticdesktop.org"><img style="border: 0px solid ; width: 180px; height: 88px;" alt="NEPOMUK Logo" src="nepomuk.png" /></a><br /> - - - - -<h1>Nepomuk Representational Language Specification</h1> - - - - -<big style="color: rgb(0, 90, 156);">Task-Force Ontologies</big> -</div> - - - - -<dl> - - - - - <dt>Latest Version:</dt> - - - - - <dd><a href="http://www.semanticdesktop.org/ontologies/2007/08/15/nrl">http://www.semanticdesktop.org/ontologies/nrl</a></dd> - - - - - <dt></dt> - - - - - <dt>This Version:</dt> - - - - - <dd><a href="http://www.semanticdesktop.org/ontologies/2007/08/15/nrl">http://www.semanticdesktop.org/ontologies/2007/08/15/nrl</a></dd> - - - - -</dl> - - - - -<dl> - - - - - <dt>Authors:</dt> - - - - - <dd>Michael Sintek, DFKI, <a href="mailto:michael.sintek@dfki.de">michael.sintek@dfki.de</a></dd> - - - - - <dd>Ludger van Elst, DFKI, <a href="mailto:elst@dfki.uni-kl.de">elst@dfki.uni-kl.de</a></dd> - - - - - <dd>Simon Scerri, DERI/NUIG, <a href="mailto:simon.scerri@deri.org">simon.scerri@deri.org</a></dd> - - - - - <dd>Siegfried Handschuh, DERI/NUIG, <a href="../htmlinformal/siegfried.handschuh@deri.org">siegfried.handschuh@deri.org</a></dd> - - - - - <dt></dt> - - - - - <dt>Editor:</dt> - - - - - <dd>Simon Scerri, DERI/NUIG, <a href="mailto:simon.scerri@deri.org">simon.scerri@deri.org</a></dd> - - - - - <dt></dt> - - - - - <dt>Contributors:</dt> - - - - - <dd>Julien Gaugaz, L3S, <a href="mailto:gaugaz@l3s.de">gaugaz@l3s.de</a> </dd> - - - - - <dd>Leo Sauermann, DFKI, <a href="mailto:leo.sauermann@dfki.de">leo.sauermann@dfki.de</a></dd> - - - - - <dd>Max Völkel, FZI, <a href="mailto:voelkel@fzi.de">voelkel@fzi.de</a><br /> - - - - - </dd> - - - - -</dl> - - - - -<dl> - - - - - <dt><span style="font-weight: bold;">Ontology:</span></dt> - - - - - <dd>XML/RDFS Serialization: <a href="http://www.semanticdesktop.org/ontologies/2007/08/15/nrl/nrl_data.rdfs">NRL -(Data Graph Only)</a></dd> - - - - - <dd>XML/RDFS Serialization: <a href="http://www.semanticdesktop.org/ontologies/2007/08/15/nrl/nrl_metadata.rdfs">NRL -(Metadata Graph Only)</a></dd> - - - - - <dd>TriG Serialization: <a href="http://www.semanticdesktop.org/ontologies/2007/08/15/nrl/nrl.trig">NRL -(Graph Set)</a></dd> - - - - -</dl> - - - - -</div> - - - - -<p class="copyright">Copyright © 2007 <a href="http://nepomuk.semanticdesktop.org/">Nepomuk Consortium</a><sup>®</sup> -This work is made available under the terms of Nepomuk <a href="LICENSE.txt">software license</a> -</p> - - - - -<hr /> -<h2><a class="mozTocH2" name="mozTocId48135"></a><a name="Abstract"></a>Abstract</h2> - - - - -<p style="text-align: justify; background-color: rgb(255, 255, 255);">NRL -was designed for knowledge representation in NEPOMUK Social Semantic -Desktop applications. While being built on top of the Resource -Description Framework (RDF) and the associated RDF Schema (RDFS), it -addresses several limitations of current Semantic Web languages, -especially with respect to modularization and costumization. These -questions seem to be important not only in Semantic Desktop scenarios -but also on the general Semantic Web. NRL tackles these questions by -including support for two main additional concepts: <a href="#3._NRL_Named_Graph_Extensions">Named Graphs</a> -and <a href="#4._Graph_Views_Extensions">Graph Views</a>. -Named graphs help coping with the heterogeneity of knowledge models and -ontologies, esp. multiple knowledge modules with potentially different -interpretations. The view concept allows for the tailoring of -ontologies towards different needs in various exploiting applications. -This view concept provides also the basic mechanism to impose different -semantics on thesame syntactical structure. <br /> - - - - -</p> - - - - -<p style="text-align: justify; background-color: rgb(255, 255, 255);"> -</p> - - - - -<h2 style="background-color: rgb(255, 255, 255);"><a class="mozTocH2" name="mozTocId695723"></a><a name="Status_of_this_document"></a>Status -of this document</h2> - - - - -<div style="background-color: rgb(255, 255, 51);" id="sotd"> -<p style="text-align: justify; background-color: rgb(255, 255, 255);"><span style="background-color: rgb(255, 255, 255);"> This document -arose from -the work of the Task-Force ontologies within the </span><a style="background-color: rgb(255, 255, 255);" href="http://nepomuk.semanticdesktop.org">Nepomuk project</a><span style="background-color: rgb(255, 255, 255);">. -It presents the specifications for the second version of the NRL -vocabulary. The document has been promoted from a draft form to this -official form upon reviewing by the general NEPOMUK consortium. -Subsequent versions of NRL might mean that the specification documents -of the later versions render this document obsolete, with respect to -the version of NRL in use, but not with respect to this versio</span>n.</p> - - - - -</div> - - - - -<div class="toc"> -<h2 id="contents"><a class="mozTocH2" name="mozTocId537771"></a><a name="Contents"></a>Contents<span style="text-decoration: underline;"></span><span style="text-decoration: underline;"></span><br /> - - - - -</h2> - - - - -<ul id="mozToc"> - - - - -<!--mozToc h2 1 h3 2 h4 3 h5 4--><li><a href="#mozTocId48135">Abstract</a></li> - - - - - <li><a href="#mozTocId695723">Status -of this document</a></li> - - - - - <li><a href="#mozTocId537771">Contents </a></li> - - - - - <li><a href="#mozTocId131741">1. -Introduction</a> - - - - <ul> - - - - - <li><a href="#mozTocId401341">1.1 -Requirements</a></li> - - - - - <li><a href="#mozTocId545385">1.2 -RDF/S and NRL -Compatibility</a></li> - - - - - <li><a href="#mozTocId290714">1.3 -Naming</a></li> - - - - - <li><a href="#mozTocId950739">1.4 -Persistence</a></li> - - - - - <li><a href="#mozTocId607548">1.5 -Social Semantic Desktop Ontologies</a></li> - - - - - <li><a href="#mozTocId976485">1.6 External -Ontology -Synchronisation</a></li> - - - - - <li><a href="#mozTocId561958">1.7 -NRL and Closed World Vs. Open World Assumptions</a></li> - - - - - - - - </ul> - - - - - </li> - - - - - <li><a href="#mozTocId154049">2. -Representing Domain Knowledge: RDF(S) and NRL Extensions to RDF(S)</a> - - - - <ul> - - - - - <li><a href="#mozTocId866477">2.1 -Resource Description -Framework -(RDF) Elements</a> - - - - <ul> - - - - - <li><a href="#mozTocId302034">2.1.1 -Classes</a></li> - - - - - <li><a href="#mozTocId861838">2.1.2 -Properties</a></li> - - - - - <li><a href="#mozTocId355985">2.1.3 -Other -Vocabulary</a></li> - - - - - - - - </ul> - - - - - </li> - - - - - <li><a href="#mozTocId794884">2.2. -RDF Schema (RDFS) -Elements</a> - - - - <ul> - - - - - <li><a href="#mozTocId679335">2.2.1 Classes</a></li> - - - - - <li><a href="#mozTocId295955">2.2.2 -Properties</a></li> - - - - - - - - </ul> - - - - - </li> - - - - - <li><a href="#mozTocId589481">2.3. -Recommendations for and -against the use of RDF/S elements</a> - - - - <ul> - - - - - <li><a href="#mozTocId522073">2.3.1 -rdfs:domain, rdfs:range</a></li> - - - - - <li><a href="#mozTocId332366">2.3.2 -Blank Nodes</a></li> - - - - - <li><a href="#mozTocId397156">2.3.3 -Collections -and Containers</a></li> - - - - - <li><a href="#mozTocId220340">2.3.4 -rdfs:isDefinedBy</a></li> - - - - - <li><a href="#mozTocId361071">2.3.5 -Reification</a></li> - - - - - - - - </ul> - - - - - </li> - - - - - <li><a href="#mozTocId932814">2.4. -Constraint Extensions</a> - - - - <ul> - - - - - <li><a href="#mozTocId770989">2.4.1. -nrl:TransitiveProperty</a></li> - - - - - <li><a href="#mozTocId779070">2.4.2. -nrl:SymmetricProperty</a></li> - - - - - <li><a href="#mozTocId832124">2.4.3. -nrl:AsymmetricProperty</a></li> - - - - - <li><a href="#mozTocId890283">2.4.4. -nrl:ReflexiveProperty</a></li> - - - - - <li><a href="#mozTocId687239">2.4.5. -nrl:FunctionalProperty</a></li> - - - - - <li><a href="#mozTocId86301">2.4.6. -nrl:InverseFunctionalProperty</a></li> - - - - - <li><a href="#mozTocId97363">2.4.7. -nrl:cardinality</a></li> - - - - - <li><a href="#mozTocId435982">2.4.8. -nrl:minCardinality</a></li> - - - - - <li><a href="#mozTocId297991">2.4.9. -nrl:maxCardinality</a></li> - - - - - <li><a href="#mozTocId72221">2.4.10. -nrl:inverseProperty</a></li> - - - - - - - - </ul> - - - - - </li> - - - - - - - - </ul> - - - - - </li> - - - - - <li><a href="#mozTocId929002">3. -Handling -Multiple Models: NRL Named Graph Extensions</a> - - - - <ul> - - - - - <li><a href="#mozTocId549245">3.1. -Graph Core Vocabulary</a> - - - - <ul> - - - - - <li><a href="#mozTocId991762">3.1.1. -nrl:Graph</a></li> - - - - - <li><a href="#mozTocId246095">3.1.2. -nrl:DocumentGraph</a></li> - - - - - <li><a href="#mozTocId178125">3.1.3. -nrl:subGraphOf</a></li> - - - - - <li><a href="#mozTocId972506">3.1.4. -nrl:superGraphOf</a></li> - - - - - <li><a href="#mozTocId503632">3.1.5. -nrl:equivalentGraph</a></li> - - - - - <li><a href="#mozTocId858885">3.1.6. -nrl:imports</a></li> - - - - - <li><a href="#mozTocId337127">3.1.7. -nrl:DefaultGraph</a></li> - - - - - - - - </ul> - - - - - </li> - - - - - <li><a href="#mozTocId787923">3.2. -Graph -Roles Vocabulary </a> - - - - <ul> - - - - - <li><a href="#mozTocId792849">3.2.1. -nrl:Data</a></li> - - - - - <li><a href="#mozTocId420122">3.2.2. -nrl:Schema</a></li> - - - - - <li><a href="#mozTocId196061">3.2.3. -nrl:InstanceBase</a></li> - - - - - <li><a href="#mozTocId287595">3.2.4. -nrl:Ontology</a></li> - - - - - <li><a href="#mozTocId372280">3.2.5. -nrl:KnowledgeBase</a></li> - - - - - <li><a href="#mozTocId379616">3.2.6. -nrl:Configuration</a></li> - - - - - <li><a href="#mozTocId781665">3.2.7. -nrl:GraphMetadata</a></li> - - - - - <li><a href="#mozTocId159397">3.2.8. -nrl:graphMetadataFor</a></li> - - - - - <li><a href="#mozTocId728175">3.2.9. -nrl:coreGraphMetadataFor</a></li> - - - - - <li><a href="#mozTocId465236">3.2.10. -nrl:Semantics</a></li> - - - - - <li><a href="#mozTocId737534">3.2.11. -nrl:hasSemantics</a></li> - - - - - <li><a href="#mozTocId331701">3.2.12. -nrl:semanticsDefinedBy</a></li> - - - - - <li><a href="#mozTocId704028">3.2.13. -nrl:semanticsLabel</a></li> - - - - - <li><a href="#mozTocId379929">3.2.14. -nrl:updatable</a></li> - - - - - - - - </ul> - - - - - </li> - - - - - <li><a href="#mozTocId54895">3. -Named Graph Example</a></li> - - - - - - - - </ul> - - - - - </li> - - - - - <li><a href="#mozTocId172834">4. Imposing -Semantics on and Tailoring of Graphs: NRL Graph Views Extensions</a> - - - - <ul> - - - - - <li><a href="#mozTocId238972">4.1. Views -Core Vocabulary</a> - - - - <ul> - - - - - <li><a href="#mozTocId304281">4.1.1. -nrl:GraphView </a></li> - - - - - <li><a href="#mozTocId595657">4.1.2. -nrl:viewOn</a></li> - - - - - <li><a href="#mozTocId124884">4.1.3. -nrl:hasSpecification </a></li> - - - - - - - - </ul> - - - - - </li> - - - - - <li><a href="#mozTocId648959">4.2. -Views Specification Vocabulary</a> - - - - <ul> - - - - - <li><a href="#mozTocId925367">4.2.1. -nrl:ViewSpecification</a></li> - - - - - <li><a href="#mozTocId162918">4.2.2. -nrl:realizes</a></li> - - - - - <li><a href="#mozTocId266518">4.2.3. -nrl:RuleViewSpecification </a></li> - - - - - <li><a href="#mozTocId718088">4.2.4. -nrl:ruleLanguage</a></li> - - - - - <li><a href="#mozTocId518283">4.2.5. -nrl:rule</a></li> - - - - - <li><a href="#mozTocId968780">4.2.6. -nrl:ExternalViewSpecification </a></li> - - - - - <li><a href="#mozTocId745751">4.2.7. -nrl:externalRealizer</a></li> - - - - - - - - </ul> - - - - - </li> - - - - - <li><a href="#mozTocId227803">4.3 -Graph Views Example</a></li> - - - - - - - - </ul> - - - - - </li> - - - - - <li><a href="#mozTocId943672">5. -Deprecated Elements</a></li> - - - - - <li><a href="#mozTocId225357">6. NRL -Semantics</a></li> - - - - - <li><a href="#mozTocId501171">References </a></li> - - - - - <li><a href="#mozTocId193273">Appendix -A. NRL Vocabulary Summary</a> - - - - <ul> - - - - - <li><a href="#mozTocId292715">A1: -Ontology Classes Description</a></li> - - - - - <li><a href="#mozTocId612656">A2: -Ontology Properties Description </a></li> - - - - - - - - </ul> - - - - - </li> - - - - -</ul> - - - - -<hr style="width: 100%; height: 2px;" /> -<h1>NRL Vocabulary Specification</h1> - - - - -<p style="text-align: justify;">This -document presents the -NEPOMUK -Representational Language (NRL), a language built on top of -RDF/S. The language is available for global use and -is independent of the domain for which it was initially designed for, -namely the [<a href="http://nepomuk.semanticdesktop.org/">NEPOMUK -Social Semantic Desktop</a>] initiative. The -NEPOMUK in -the language name (NRL) has been -retained only for historic purposes. Information regarding other -NEPOMUK ontologies can be found in [<a href="#1.5_Semantic_Desktop_Ontologies">Section -1.5</a>]. </p> - - - - -<p style="text-align: justify;">The -document stucture is as -follows. [<a href="#1._Introduction">Section 1</a>] gives -an insight -on the motivation for this work, the approaches taken, some resulting -assumptions and the specificatin of general naming and persistance -policies. [<a href="#2._Imported_Vocabulary_Elements">Section -2</a>] -gives an overview of the imported RDF/S vocabulary elements, -some of which have been restricted, and the NRL <span style="font-style: italic;">Constraint Extensions</span> -to -RDF/S. <span style="font-style: italic;"></span></p> - - - - -<p style="text-align: justify;"><span style="font-style: italic;">Named -Graph Extensions </span>[<a href="#3._NRL_Named_Graph_Extensions">Section -3</a>] gives an overview <span style="font-style: italic;"></span>of -the NRL -vocabulary to model the handling of multiple models, while <span style="font-style: italic;">Graph -View Extensions</span> -[<a href="#4._Graph_Views_Extensions">Section -4</a>] presents the vocabulary available to tailor and impose -semantics on named graphs.</p> - - - - -<p style="text-align: justify;">[<a href="#5._Deprecated_Elements">Section 5</a>] -is dedicated to deprecated elements whereas [<a href="#6._NRL_Semantics">Section -6</a>] -defines -the formal semantics of NRL (to be completed). A summary of all the NRL -vocabulary elements is given in [<a href="#Appendix_A._NRL_Vocabulary_Summary">Appendix A</a>].</p> - - - - -<h2><a class="mozTocH2" name="mozTocId131741"></a><a name="1._Introduction"></a>1. -Introduction</h2> - - - - -<span style="font-weight: bold;"></span> -<p style="text-align: justify;"><span style="font-weight: normal;"></span><span style="background-color: rgb(255, 255, 255);">NRL -is based on a number of key concepts, some of which -are -identical to concepts defined in earlier work. Other concepts -are -fundamentally the same to ones in existant work, but differ slightly in -definition, while some concepts are a fresh approach to data -representation. The key concepts are <span style="font-style: italic;">RDF -triple</span>, <span style="font-style: italic;">Named -Graph</span> -and <span style="font-style: italic;">Graph Views</span> and -they are introduced in this section.</span></p> - - - - -<p style="text-align: justify;"><span style="background-color: rgb(255, 255, 255);"></span><span style="background-color: rgb(255, 255, 255);"></span><span style="background-color: rgb(255, 255, 255);">The basic -concept is the <span style="font-style: italic;">RDF -triple</span> and the definition is fundamentally similar to the -one given in [</span><a style="background-color: rgb(255, 255, 255);" href="#References">RDF -Specification - CONCEPTS</a><span style="background-color: rgb(255, 255, 255);">] where a -triple consists of three components:</span></p> - - - - -<ul style="text-align: justify;"> - - - - - <li><span style="background-color: rgb(255, 255, 255);"></span><span style="background-color: rgb(255, 255, 255);"></span>a -subject - in the form of a URI Reference</li> - - - - - <li>a predicate - in the form of a URI Reference</li> - - - - - <li>an object - in the form of either a URI Reference or a -literal</li> - - - - -</ul> - - - - -<div style="text-align: justify;"><span style="background-color: rgb(255, 255, 255);">where -the predicate denotes the relationship between the subject and the -object. The only difference is that in NRL it is not expected -that -a blank node manifests itself as either a subject or an object -of -a triple [See <a href="#2.3.2_Blank_Nodes">Recommendation2.3.2</a>]. -</span><span style="background-color: rgb(255, 255, 255);"></span><br /> - - - - -<span style="background-color: rgb(255, 255, 255);"></span></div> - - - - -<p style="text-align: justify;"><span style="background-color: rgb(255, 255, 255);">An <span style="font-style: italic;">RDF Graph</span> -consists of a set of triples. The definition is similar to -the one given in [</span><a style="background-color: rgb(255, 255, 255);" href="#References">RDF -Specification - -CONCEPTS</a><span style="background-color: rgb(255, 255, 255);">].</span><span style="background-color: rgb(255, 255, 255);"> A </span><span style="font-style: italic; background-color: rgb(255, 255, 255);">Named -Graph </span><span style="background-color: rgb(255, 255, 255);">is -an RDF Graph identified by a name. In NRL, all RDF triples -must be assigned -to at least one named graph. Triples that are not, are automatically -assigned to a special named graph, the [<a href="#3.1.7._nrl:DefaultGraph">nrl:DefaultGraph</a>]. -Therefore, NRL -data handling is usually defined in terms of named graphs rather than -RDF triples. The formal definition for a named graph is the same as -that -given in [</span><a style="background-color: rgb(255, 255, 255);" href="#References">NAMED -GRAPHS</a><span style="background-color: rgb(255, 255, 255);">] -but excludes the open-world assumption [See <a href="#1.7_NRL_and_Closed_World_Vs._Open_World">Section 1.7</a>]. -Named graphs differ in content and purpose, -and for this reason <span style="font-style: italic;">Graph -Roles </span>have -been introduced, representing general roles like simple data, ontology, -knowledge base, plus other less generic roles. Graph roles carry <span style="font-style: italic;">Declarative Semantics</span>, -which means that their semantics are implicit and have not necessarily -been realized (in the form of inferred triples). A more elaborate -definition, syntax -specification and example section for named graphs is given in -</span><span style="font-style: italic; background-color: rgb(255, 255, 255);">Named -Graph Extensions </span><span style="background-color: rgb(255, 255, 255);">[</span><a style="background-color: rgb(255, 255, 255);" href="#3._NRL_Named_Graph_Extensions">Section -3</a><span style="background-color: rgb(255, 255, 255);">].</span></p> - - - - -<p style="text-align: justify;"><span style="background-color: rgb(255, 255, 255);"></span><span style="background-color: rgb(255, 255, 255);"></span><span style="background-color: rgb(255, 255, 255);">A named graph -consists of the corresponding triple set as is, and retrieving -RDF triples from a named graph, will simply return the enumerated -triples -in the set. However </span><span style="background-color: rgb(255, 255, 255);">it -is frequently required to work with graphs having realized -semantics in -the form of entailment triples, according to some declared -semantics. Additionaly, it is sometimes required to work with -more -abstract, simplified forms of a graph. In general, it is useful to work -with various interpretations of a named graph in different situations.</span><span style="background-color: rgb(255, 255, 255);"> -However, in order to preserve the integrity and consistency of named -graphs, an original named graph should be independent of -its interpretations. To model -this, one can -define arbitrary views which realize different -interpretations for an established named graph. We call these -interpretations </span><span style="font-style: italic; background-color: rgb(255, 255, 255);">Graph -Views </span><span style="background-color: rgb(255, 255, 255);">and -they -are formally defined in </span><span style="font-style: italic; background-color: rgb(255, 255, 255);">Graph -Views Extensions </span><span style="background-color: rgb(255, 255, 255);">[</span><a style="background-color: rgb(255, 255, 255);" href="#4._Graph_Views_Extensions">Section -4</a><span style="background-color: rgb(255, 255, 255);">]. -Graph views are themselves named -graphs, so it -is possible for a view to be applied on top of another graph -view. <span style="font-style: italic;">View -Specifications</span> define how a view </span>is -to be computed and they can refer either to a set of rules in some rule -language, or to an external application. Some view specifications -realize the <span style="font-style: italic;">Procedural -Semantics</span> of a graph, and the result is a <span style="font-style: italic;">Semantic View</span>, -having both declarative and procedural semantics. <span style="background-color: rgb(255, 255, 255);">Conceptually, -a graph <span style="font-style: italic;">g</span> </span><span style="background-color: rgb(255, 255, 255);">can be given a -semantics by applying a semantic realizing view</span><span style="font-style: italic; background-color: rgb(255, 255, 255);"> v</span><span style="background-color: rgb(255, 255, 255);">,</span><span style="font-style: italic; background-color: rgb(255, 255, 255);"> -</span><span style="background-color: rgb(255, 255, 255);">which -is linked to some semantic specifications. Practically, if the -semantics specifications are those for NRL, and these state that some -of the applied semantics </span><span style="background-color: rgb(255, 255, 255);">are -transitive (e.g. rdfs:subClass) this would imply that <span style="font-style: italic;">v</span></span><span style="font-style: italic; background-color: rgb(255, 255, 255);"> -</span><span style="background-color: rgb(255, 255, 255);">will -be the extension of </span><span style="background-color: rgb(255, 255, 255); font-style: italic;">g</span><span style="background-color: rgb(255, 255, 255);"> with the -inferred triples generated by performing the transitive closure.</span></p> - - - - -<p style="text-align: justify;"><span style="background-color: rgb(255, 255, 255);"></span><span style="background-color: rgb(255, 255, 255);"></span> -<span style="background-color: rgb(255, 255, 255);">The -following -figure </span><span style="background-color: rgb(255, 255, 255);"></span><span style="background-color: rgb(255, 255, 255);">presents the -important aspects of the NRL language, including the key concepts just -described and their relationships. The -diagram is partitioned in the (abstract) -syntax on which it is defined (right), and the formal semantics (left) -to which it is linked to. </span><span style="background-color: rgb(255, 255, 255);">The -NRL domain is depicted by the grey shaded part. Notice that NRL is not -limited to the syntax partition, since it includes NRL formal semantics -defined in [<a href="#6._NRL_Semantics">Section -6</a>]. </span><span style="background-color: rgb(255, 255, 255);">The -NRL syntax -is -composed of a base langugage and a schema language. The base -language refers to the specification of the key concepts in -the -language, including named graphs, graph roles and graph views -while </span><span style="background-color: rgb(255, 255, 255);">t</span><span style="background-color: rgb(255, 255, 255);">he schema -language (NRL Schema) provides the means to define schemas (especially -information models and ontologies). </span><span style="background-color: rgb(255, 255, 255);">The semantics -partition mainly distinguishes between abstract declarative semantics, -and realized procedural semantics.</span><br /> - - - - -</p> - - - - -<div style="text-align: center;"> -<div style="text-align: justify; margin-left: 40px;"> -<div style="text-align: center;"><img style="width: 547px; height: 330px;" alt="Overview of NRL: AbstractSyntax, Concepts and Semantics" src="NRLoverview.png" /><br /> - - - - -</div> - - - - -<div style="text-align: center;"><a name="Fig1"></a>Figure -1: Overview of NRL - -Abstract Syntax, Concepts and Semantics<br /> - - - - -</div> - - - - -<br /> - - - - -</div> - - - - -<div style="text-align: justify;"> -<p>The syntax schema consists of the NRL Schema, which is based -on an -extended RDFS (RDFS'). The syntax base presents the key -concepts of NRL as a set abstraction. Named graphs, consisting of RDF -Triples, are the most general set (red) since both graph roles and -graph views are special kinds of named graphs. Graph Roles (yellow) are -tied to declarative semantics that they assume (e.g. an ontology using -elements from RDF/S). Graph Views (green) are tied to view -specifications which execute the view's realization. The -intersection between graph roles and graph views refers to semantic -views. These special views realize the declarative semantics of the -graph role they are interpreting (e.g. by extending an ontology that -uses <span style="font-style: italic;">rdfs:subClassOf</span> -by its transitive closure as defined in RDF/S Semantics). Thus, as -shown on the left hand side of the figure, semantic view specifications -carry the realized procedural semantics for a view, which are -linked to the abstract declarative semantics of a language.<span style="background-color: rgb(255, 255, 255);"><br /> - - - - -</span></p> - - - - -</div> - - - - -<div style="text-align: justify;"> -<p><span style="background-color: rgb(255, 255, 255);"><a href="#Fig2">Figure 2</a></span><span style="background-color: rgb(255, 255, 255);"> shows how the -theoritical basis of NRL can be -applied in practice to handle RDF data. Data handling includes -creation, merging, interpretation and presentation of RDF data. It -presents the dataflow for some typical NRL data and how the various -concepts introduced earlier can be effectively used to model RDF data -and use it in different scenarios in a sound but intuitive way. The -example sections for the Named Graph extensions [<a href="#3.3._Named_Graph_Example">Section 3.3</a>] and -the Graph Views extensions [<a href="#4.3_Graph_Views_Example">Section -4.3</a>] present examples that model the dataflow in this figure -in TriG syntax </span>[<a href="#References">TRIG</a>]. -TriG is a straight-forward -extension of Turtle -[<a href="#References">TURTLE</a>]. Turtle itself -is an extension of N-Triples [<a href="#References">N-TRIPLES</a>] -which carefully takes the most useful and appropriate things added from -Notation3 -[<a href="#References">NOTATION3</a>] -while keeping it in the RDF model. TriG is a plain text -format created for serializing NGs and RDF Datasets.<br /> - - - - -</p> - - - - -</div> - - - - -<div style="text-align: justify;"> -<p><span style="background-color: rgb(255, 255, 255);">The -dataflow is based on four existing named graphs, two having the -role of [<a href="#3.2.4._nrl:Ontology">nrl:Ontology</a>] -(ontologies </span><span style="background-color: rgb(255, 255, 255);"><span style="font-style: italic;">O</span><small style="font-style: italic;"><small><small>1</small></small></small> -and <span style="font-style: italic;">O</span><small style="font-style: italic;"><small><small>2</small></small></small></span><span style="background-color: rgb(255, 255, 255);">) and the -other two that of [<a href="#3.2.3._nrl:InstanceBase">nrl:InstanceBase</a>] -(instance bases </span><span style="background-color: rgb(255, 255, 255);"><span style="font-style: italic;">I</span><small style="font-style: italic;"><small><small>1</small></small></small> -and <span style="font-style: italic;">I</span><small style="font-style: italic;"><small><small>2</small></small></small></span><span style="background-color: rgb(255, 255, 255);">). A new named -graph, <span style="font-style: italic;">O</span>, -is also defined as having the role of </span><span style="background-color: rgb(255, 255, 255);">[<a href="#3.2.4._nrl:Ontology">nrl:Ontology</a>]</span><span style="background-color: rgb(255, 255, 255);"> and by using -the property [<a href="#3.1.6._nrl:imports">nrl:imports</a>] -it is defined as being the supergraph of both </span><span style="background-color: rgb(255, 255, 255);"><span style="font-style: italic;">O</span><small style="font-style: italic;"><small><small>1</small></small></small> -and <span style="font-style: italic;">O</span><small style="font-style: italic;"><small><small>2</small></small></small></span><span style="background-color: rgb(255, 255, 255);">. This -constitutes an ontology merge for <span style="font-style: italic;">O</span></span><span style="background-color: rgb(255, 255, 255);"><span style="font-style: italic;"></span><small style="font-style: italic;"><small><small>1</small></small></small> -and <span style="font-style: italic;">O</span><small style="font-style: italic;"><small><small>2</small></small></small></span><span style="background-color: rgb(255, 255, 255);"> into <span style="font-style: italic;">O</span>.</span><span style="background-color: rgb(255, 255, 255);"></span> -Similarly, a new named graph, <span style="font-style: italic;">KB</span>, -is defined to have the role of [<a href="#3.2.5._nrl:KnowledgeBase">nrl:KnowledgeBase</a>] -and is defined as the supergraph of <span style="font-style: italic;">O</span>, <span style="font-style: italic;">I</span><small style="font-style: italic;"><small>1</small></small> -and <span style="font-style: italic;">I</span><small style="font-style: italic;"><small>2</small></small>. -Therefore,<span style="font-style: italic;"> KB </span>consists -of all RDF triples in <span style="background-color: rgb(255, 255, 255);"></span><span style="background-color: rgb(255, 255, 255);"></span><span style="background-color: rgb(255, 255, 255);"><span style="font-style: italic;">O</span><small style="font-style: italic;"><small><small>1</small></small></small>, -<span style="font-style: italic;">O</span><small style="font-style: italic;"><small><small>2</small></small></small></span>, -<span style="font-style: italic;">I</span><small style="font-style: italic;"><small>1</small></small> -and<span style="font-style: italic;"> I</span><small><small><span style="font-style: italic;">2</span><big><big>. -</big></big></small></small></p> - - - - -</div> - - - - -<img style="width: 552px; height: 339px;" alt="NRL Dataflow" src="dataflow.png" /><br /> - - - - -<br /> - - - - -<a name="Fig2"></a>Figure 2: NRL Dataflow diagram<br /> - - - - -<div style="text-align: left;"> -<div style="text-align: justify; margin-left: 0px; width: 900px;"> -<p><small><small><big><big>An -RDF programmer would like to work with an extension of <span style="font-style: italic;">KB</span> that includes -also the realized semantics that <span style="font-style: italic;">KB</span> -is implicitly carrying. To generate this extension, or view, the RDF -programmer can define an instance of [<a href="#4.2.1._nrl:ViewSpecification">nrl:ViewSpecification</a>] -that computes and returns -the procedural semantics for <span style="font-style: italic;">KB</span>. -</big></big></small></small><big><span style="background-color: rgb(255, 255, 255);"></span></big>The -view specification uses a rule language of choice that provides a -number of rules, one of which computes the transitive closure of <span style="font-style: italic;">rdfs:subClassOf</span>, as -defined in the RDFS semantics, for a set of RDF triples. Executing the -chosen rules over the triples in <span style="font-style: italic;">KB</span> -result in a semantic view <span style="font-style: italic;">RDFS(KB)</span> -consisting of the RDF triples in <span style="font-style: italic;">KB</span> -plus the generated entailment triples.</p> - - - - -<p>Next, the RDF programmer needs to present some of -this -extended data to an average user in a simplified way. In particular, -the user would at some point like to see the class hierarchy present in -<span style="font-style: italic;">RDFS(KB)</span>. -The RDF programmer can create external view specifications, in the form -of applications which take a named graph as input (a set of -RDF triples), and return the desired RDF triples as output. In -this case, an external view specification, <span style="font-style: italic;">E<small><small>1</small></small></span>, -is created and designed to select and return the triples defining the -class hierarchy within an input named graph. The view generated by this -application, <span style="font-style: italic;">E<small><small>1</small></small>(RDFS(KB)), -</span>which is basically another named graph, is -the data required for presentation to the user. It is worth to -note, that at this stage, all the seven named graphs that this last view<span style="font-style: italic;"> </span>is generated upon -are still intact and they have not been modified by any of the -operations. </p> - - - - -<h3><a class="mozTocH3" name="mozTocId401341"></a><a name="1.1_Requirements"></a>1.1 -Requirements</h3> - - - - -<p style="text-align: justify;">In this section we -specify the original identified requirements for a -Representational Language (excluding requirements that are -domain-dependent) and whether their fulfillment was successful or -otherwise.</p> - - - - -<p style="text-align: justify;">The following -requirements have been satisfied:</p> - - - - -<ul> - - - - - <li>Tool support for inferencing, interpretation, -manipulation and storage.</li> - - - - - <li>NRL should allow for validation of ontologies.</li> - - - - - <li>Basic subClassOf, type, and inverseProperty inference has -to be computable efficiently.</li> - - - - - <li>Domain and Range properties must be adhered to and -verified. [See domain and range usage <a href="#2.3._Recommendations">restrictions</a>]</li> - - - - - <li>Properties must support cardinality requirements. [See <a href="#2.4.7._nrl:cardinality"> nrl:cardinalty</a>, <a href="#2.4.8._nrl:minCardinality">nrl:minCardinalty</a> -and <a href="#2.4.9._nrl:maxCardinality">nrl:maxCardinality</a>]</li> - - - - - <li>Representation of ontology models. [See -graph role <a style="background-color: rgb(255, 255, 255);" href="#3.2.4._nrl:Ontology">nrl:Ontology</a>]</li> - - - - - <li>Ontology imports must be possible. Ontology management -must -be provided. [See named graph property [<a style="background-color: rgb(255, 255, 255);" href="#3.1.6._nrl:imports">nrl:imports</a>]</li> - - - - - <li>Support for Quads/Named Graphs to record provenance. [See <a href="#3._NRL_Named_Graph_Extensions">Named -Graph -Extensions</a>]</li> - - - - -</ul> - - - - -<p style="text-align: justify;">The following -requirements are no longer in the scope of the -NRL but in that of lower-level ontologies:</p> - - - - -<ul> - - - - - <li>The language must differentiate between concepts and -web-resources. [See <a href="#5._Deprecated_Elements">nrl:Thing</a> -and <a href="#5._Deprecated_Elements">nrl:ResourceManifestation</a>]</li> - - - - - <li>Meta-modeling needs to be supported. [See <a href="#5._Deprecated_Elements">nrl:NRLClass</a> -and <a href="#5._Deprecated_Elements">nrl:NRLProperty</a>]</li> - - - - - <li>Support for alternative labels (thesauri helpers) -alongside -labels is required. [See alternative labels property <a href="#5._Deprecated_Elements">nrl:altLabel</a>]</li> - - - - - <li>n-ary relations should be supported. [See <a href="#5._Deprecated_Elements"> -nrl:relationProperty</a>]</li> - - - - - <li>It must provide some basic semantic relations. [See <a href="#5._Deprecated_Elements">nrl:partOf</a>, <a href="#5._Deprecated_Elements">nrl:hasTopic</a> -and <a href="#5._Deprecated_Elements"> -nrl:relationProperty</a>]</li> - - - - - <li>Typing on reifications and contexts.</li> - - - - -</ul> - - - - -<p style="text-align: justify;">The following -requirements have not been satisfied:</p> - - - - -<ul> - - - - - <li>Support for imprecise/fuzzy/probabilistic -representations.</li> - - - - -</ul> - - - - -<p><span style="font-style: italic; font-weight: bold;">Note</span><span style="font-weight: bold;">:</span> -The -fulfillment of this requirement will be postponed until -a non-imprecise version of NRL is stable.</p> - - - - -<p>The following -requirement has been retracted:</p> - - - - -<ul> - - - - - <li>Typing on container -contents. Containers are to be -avoided -altogether. [See Recommendation <a href="#2.3.3_Grouping_resources">2.3.3</a>]</li> - - - - -</ul> - - - - -<h3><a class="mozTocH3" name="mozTocId545385"></a><a name="1.2_RDFS_and_NRL_Compatibility"></a>1.2 -RDF/S and NRL -Compatibility</h3> - - - - -<p style="text-align: justify;">This specification -provides some recommendations as to the use -of some RDF/S elements or constructs [<a href="#2.3">2.3</a>]. -It must be noted that if these recommendations are not followed, this -still results in <i>legal</i> RDF/S data and therefore <i>legal</i> -NRL data. However this does not imply that such data would be <i>valid</i> -NRL data. Although such data would conform to the RDF/S specifications, -correct manipulation of invalid NRL data is not guaranteed if the -recommendations are not followed. This also applies to RDF/S data that -is imported -in an NRL context (e.g. RDF/S data imported on one's semantic desktop). -In a more technical sense, legal NRL would be processed without -generating errors, but only valid NRL would be processed without -generating warnings. </p> - - - - -<p style="background-color: rgb(255, 255, 255); text-align: justify;"><span style="background-color: rgb(255, 255, 255);">Since -NRL is based on the Named Graph paradigm [See </span><a style="background-color: rgb(255, 255, 255);" href="#3._NRL_Named_Graph_Extensions">Named -Graph Extensions</a><span style="background-color: rgb(255, 255, 255);">], NRL -data cannot be directly represented with plain RDF/S since NG's are an -extension </span><span style="font-style: italic; background-color: rgb(255, 255, 255);">on -top</span><span style="background-color: rgb(255, 255, 255);"> -of RDF/S. Therefore NRL with named graphs is not backward -compatible -to RDF/S. It is compatible however with Named Graphs -as specified in [</span><a style="background-color: rgb(255, 255, 255);" href="#References">SPARQL-QUERY</a><span style="background-color: rgb(255, 255, 255);">].</span><br /> - - - - -</p> - - - - -<h3><a class="mozTocH3" name="mozTocId290714"></a><a name="1.3_Naming"></a>1.3 -Naming</h3> - - - - -<p style="text-align: justify;">The URI for the NRL -Vocabulary is <a href="http://www.semanticdesktop.org/ontologies/nrl#">http://www.semanticdesktop.org/ontologies/yyyy/mm/dd/nrl#</a> -subject -to the date of the latest stable version.</p> - - - - -<p style="text-align: justify;">The URI for an element -in the vocabulary is constructed by -appending a fragment identifier to the above URI. A fragment identifier -for a class always starts with an uppercase letter while in the case of -properties it starts with a lowercase letter. In the case of class -identifiers consisting of multiple words, the leading character of each -word will be an uppercase letter. In case of property identifiers -consisting of multiple words, the leading character of each word will -be an uppercase letter, except for the first word which as specified -should be in lowercase.</p> - - - - -<i>Examples<br /> - - - - -<br /> - - - - -</i> -<table style="text-align: left; width: 100%; height: 83px;" border="1" cellpadding="2" cellspacing="2"> - - - - - <tbody> - - - - - <tr> - - - - - <td><span style="font-family: monospace;">http://www.semanticdesktop.org/ontology/yyyy/mm/dd/nrl#Class</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">http://www.semanticdesktop.org/ontology/yyyy/mm/dd/nrl#ExampleClass</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">http://www.semanticdesktop.org/ontology/yyyy/mm/dd/nrl#property</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">http://www.semanticdesktop.org/ontology/yyyy/mm/dd/nrl#exampleProperty</span></td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<br /> - - - - -<h3><a class="mozTocH3" name="mozTocId950739"></a><a name="1.4_Persistence"></a>1.4 -Persistence</h3> - - - - -<p>The NRL Vocabulary specification defined here and any -previous -or later versions, plus the NRL ontology itself [<a href="http://nepomuk.org/ontologies/nrl">http://www.semanticdesktop.org/ontology/yyyy/mm/dd/nrl#</a>] -will be provided as persistent resources.</p> - - - - -<h3><a class="mozTocH3" name="mozTocId607548"></a><a name="1.5_Social_Semantic_Desktop_Ontologies"></a>1.5 -Social Semantic Desktop Ontologies</h3> - - - - -<p style="text-align: justify;">Ontologies are -structured in various layers or levels, with -the rationale that those at higher levels are more stable and thus -change less often than those at lower levels. Usually, one -distinguishes representational ontologies, upper-level ontologies, -mid-level ontologies, and domain ontologies.</p> - - - - -<p style="text-align: justify;">The NRL is a -representational ontology and although it is -domain independent it was designed to fulfil requirement for the -NEPOMUK Social Semantic Desktop initiative. Representational ontologies -define -the vocabulary with which other ontologies are represented. Other -examples of such representational ontologies are RDF/S and OWL. The -relationship of a representational ontology to other ontologies is -quite different from the relationship between the other ontologies -themselves. While upper-level ontologies generalize mid-level -ontologies, which in turn generalize domain ontologies, all these -ontologies can be seen as <i class="italic">instances</i> -of the -representational ontology.</p> - - - - -<p style="text-align: justify;">The specification of -various other ontologies is in the -pipeline for the Social Semantic Desktop project. In particular, -the -following (upper-level) ontologies are being discussed:</p> - - - - -<ul> - - - - - <li>Information Element -Ontology [<a href="http://www.semanticdesktop.org/ontologies/nie">NIE</a>] -- to handle physical -resource (e.g. documents, web pages, files etc.)</li> - - - - - <li>Annotation Ontology -[<a href="http://www.semanticdesktop.org/ontologies/nao">NAO</a>] - -to handle general -annotation (e.g. Data annotation, Linking abstract -to physical resources) as well as graph -annotation (e.g. Data -authorship. etc.)</li> - - - - - <li>Personal Information Modelling Ontology [PIMO] - to model -things and relationships on the user's desktop.</li> - - - - -</ul> - - - - -<h3><a class="mozTocH3" name="mozTocId976485"></a><a name="1.6_External_Ontology_Synchronisation"></a>1.6 External -Ontology -Synchronisation</h3> - - - - -<p>The ontologies resulting -from the Social Semantic Desktop project -are -partly inspired by existing elements in external ontologies. -As a result some elements are very -similar to elements in existing languages like OWL <a href="#References">[OWL Overview]</a> and OMV <a href="#References">[OMV Documentation]</a>. -Also, some RDF/S elements do not fulfil the requirements for the -project's ontologies and therefore problems arise from these two -scenarios. When requiring elements that already exist in some other -standard ontology, but do not exactly conform to our requirements, -there are the following three outlined options:</p> - - - - -<ol> - - - - - <li>Re-define semantics for use within NEPOMUK ontologies.</li> - - - - -</ol> - - - - -This creates major problem when it comes to heterogeneity -issues. One cannot redefine an element if it already has a defined -semantics, because when encountering such an element, it would not -be -possible to decide in which context to interpret it. Restrictions are a -more subtle form of redefinition. In this case, any restrictions placed -on the use of existing elements will result in the possibility of -having Legal but Invalid data in the NEPOMUK ontologies context. See -further discussions in [<a href="#1.2">1.2</a>] -in -the case of NRL. -<ol style="text-align: justify;"> - - - - - <li value="2">Re-create new elements with required -semantics and ignore the existing ones.</li> - - - - -</ol> - - - - -<div style="text-align: justify;"> -This goes against the idea of ontologies and the Semantic -Web in general, that is, to have a shared conceptualisation, promote -the re-use of ontologies and discourage the re-creation of data. -<ol style="text-align: justify;"> - - - - - <li value="3">Re-create new elements with required -semantics and provide a mapping between them and the existing elements.</li> - - - - -</ol> - - - - -</div> - - - - -<div style="text-align: justify;"> -This option is a variant of the previous option, where -although new elements are re-created, the relation between the new and -the existent elements is modelled using mappings. Examples of these -mappings are subclass, hyponym, meronym. Although in this case, new -elements satisfying the requirements are created, the existent elements -are not ignored and therefore the shared conceptualisation ideology is -respected. -<p style="text-align: justify; width: 900px;">In the -NEPOMUK -ontologies, option three is the standard -best practice when existent elements with different semantics are -required. When requiring restriction on the use of elements, option one -is sufficient since it does not violate the predefined semantics. -However in this case the statement in [<a href="#1.2">1.2</a>] -should be noted. The mapping constructs required for option three will -be defined over time and therefore, although theoritically the -agreed-upon option is three, in practice option two is currently being -implemented.</p> - - - - -</div> - - - - -<h3><a class="mozTocH3" name="mozTocId561958"></a><a name="1.7_NRL_and_Closed_World_Vs._Open_World"></a>1.7 -NRL and Closed World Vs. Open World Assumptions</h3> - - - - -<div style="width: 909px;"> -<div style="text-align: justify; width: 900px;"> -<div style="text-align: justify;"> -<p style="width: 900px;">The open-world -assumption (OWA) presumes that its knowledge of the -world is incomplete and that this lack of knowledge does not imply -falsity. On the other hand, the closed-world assumption (CWA) presumes -that what is not currently known to be true, is false. Whereas the OWA -states that everything that is not known is undefined, the CWA implies -that everything we don't know is false. </p> - - - - -</div> - - - - -<p>This assumption has a big impact on direct and indirect -knowledge -generated through RDF data. This difference is demonstrated through the -following example which is based on <a href="#3._NRL_Named_Graph_Extensions">Named -Graphs</a> -and -<a href="http://www.wiwiss.fu-berlin.de/suhl/bizer/TriG/">TriG</a> -[TRIG]. We will consider the implications of importing the given three -graphs <span style="font-style: italic;">g1</span>, -<span style="font-style: italic;">g2</span> and <span style="font-style: italic;">g3</span> into an external -graph <span style="font-style: italic;">g</span>.</p> - - - - -<table style="text-align: left; width: 100%; height: 463px;" border="1" cellpadding="2" cellspacing="2"> - - - - - <tbody> - - - - - <tr> - - - - - <td><span style="font-family: monospace;">@prefix -nrl: -<http://www.semanticdesktop.org/ontology/yyyy/mm/dd/nrl#> -.</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> @prefix dom: -<http://www.example.org/ontology/domainOntology#> . </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> @prefix ex: -<http://www.example.org/vocabulary#> .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> @prefix ex2: -<http://www.example.org/vocabulary#> .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> @prefix : -<http://www.example.org/vocabulary#> .</span><br /> - - - - - <br /> - - - - - <span style="font-family: monospace;">[1] :g1 {</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - dom:Person rdf:type rdfs:Class .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - dom:Man rdf:type rdfs:Class ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - rdfs:subClassOf -dom:Person .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - dom:Woman rdf:type rdfs:Class ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - rdf:subClassOf -dom:Person .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - dom:hasFather rdf:type rdf:Property ,</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - - nrl:FunctionalProperty ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdfs:domain rdf:Person ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdfs:range rdf:Man . }</span><br style="font-family: monospace;" /> - - - - - <br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[2] :g2 { </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ex:Peter rdf:type dom:Man .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ex:Jill rdf:type dom:Person ; </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - dom:hasFather -ex:Peter . }</span><br style="font-family: monospace;" /> - - - - - <br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[3] :g3 { </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ex2:Jack rdf:type dom:Man .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ex:Jill dom:hasFather ex2:Jack . } </span></td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -</div> - - - - -</div> - - - - -<div style="width: 909px;"> -<br /> - - - - -[1] The first -graph consists of an ontology and presents -three classes and a property. The classes are <span style="font-style: italic;">dom:Person</span> and its -two subclasses <span style="font-style: italic;">dom:Woman</span> -and <span style="font-style: italic;">dom:Man</span>. -The property <span style="font-style: italic;">dom:hasFather </span>is -a <a href="#2.4.5._nrl:FunctionalProperty">nrl:FunctionalProperty</a> -applicable to class <span style="font-style: italic;">dom:Person -</span>and taking as values instances of <span style="font-style: italic;">dom:Man</span>.<br /> - - - - -<br /> - - - - -</div> - - - - -<div style="width: 909px;"> -[2] The second named graph is an instance base consisting of -two -instances, <span style="font-style: italic;">Peter </span>as -a <span style="font-style: italic;">dom:Man </span>and <span style="font-style: italic;">Jill</span> as a <span style="font-style: italic;">dom:Person</span>. In -addition, the <span style="font-style: italic;">dom:hasFather</span> -relation between <span style="font-style: italic;">Jill </span>and<span style="font-style: italic;"> Peter</span> says that <span style="font-style: italic;">Peter</span> is <span style="font-style: italic;">Jill</span>'s father. -</div> - - - - -<div style="width: 909px;"> -<span style="font-style: italic;">Question</span>: -Is <span style="font-style: italic;">Jill</span> a <span style="font-style: italic;">dom:Woman</span>?<span style="font-style: italic;"></span> -<br /> - - - - -<span style="font-style: italic;">OWA</span>: -Unknown - It is only known that <span style="font-style: italic;">Jill</span> -is a <span style="font-style: italic;">dom:Person</span>. -OWA cannot determine whether the statement is true or false. -</div> - - - - -<div style="text-align: justify;"> -<span style="font-style: italic;">CWA</span>: -No - <span style="font-style: italic;">Jill </span>is -nowhere -defined to be a <span style="font-style: italic;">dom:Woman</span>. -Therefore the statement is false. -<br /> - - - - -<br /> - - - - -<span style="font-style: italic;">Question</span>: -Is <span style="font-style: italic;">Peter</span> a -<span style="font-style: italic;">dom:Person</span>? -<br /> - - - - -<span style="font-style: italic;">OWA</span>: -Yes - -Peter is a <span style="font-style: italic;">dom:Man</span>, -and this is a subclass of <span style="font-style: italic;">dom:Person</span>. -<br /> - - - - -<span style="font-style: italic;">CWA</span>: -Yes - -Peter is a <span style="font-style: italic;">dom:Man</span>, -and this is a subclass of <span style="font-style: italic;">dom:Person</span>.<br /> - - - - -<br /> - - - - -[3] -The -third graph is also an instance base and presents another instance, <span style="font-style: italic;">Jack </span>as a <span style="font-style: italic;">dom:Man</span>. The same <span style="font-style: italic;">Jill </span>defined in -graph two, is said to have <span style="font-style: italic;">Jack</span> -as her father<span style="font-style: italic;">.</span><br /> - - - - -<span style="font-style: italic;"></span><span style="font-style: italic;"></span><br /> - - - - -Since <span style="font-style: italic;">dom:hasFather </span>is -a functional property, <span style="font-style: italic;">Jill -</span>can have only one person related to her by that property. -<span style="font-style: italic;"></span><br /> - - - - -<span style="font-style: italic;">OWA</span>: -It -results that <span style="font-style: italic;">Jack</span> -and <span style="font-style: italic;">Peter</span> -are the same person. This statement is implicitly added to the -data. -<span style="font-style: italic;"></span><br /> - - - - -<span style="font-style: italic;">CWA</span>: -There -is conflicting data in g2 and g3. An error is generated. -<p>The RDF -language itself assumes an open-world and so does -the definition for Named Graphs in <span style="background-color: rgb(255, 255, 51);"><span style="background-color: rgb(255, 255, 255);">[</span></span><a style="background-color: rgb(255, 255, 255);" href="#References">NAMED -GRAPHS</a><span style="background-color: rgb(255, 255, 255);">]. -There is a difference of opinion on what approach is best for handling -RDF data. While OWA is more flexible, and more likely to -generate -new statements based on ones that already exist in the models, its -non-monotonic nature hinders computability and largely increases -the -complexity of RDF data. On the other hand, while CWA is much more prone -to generate errors, it is totally deterministic and one can always -compute whether any statement under the assumption is true or false.</span></p> - - - - -<p><span style="background-color: rgb(255, 255, 255);"></span>Although -it is sometimes more realistic to apply OWA, the correctness -of this approach is not guaranteed. In the given example, it might -makes sense to leave the possibility open for the statement <span style="font-style: italic;">Jill is a woman</span> to -be true. However it might not make sense to assume that the fact <span style="font-style: italic;">Jack is Peter</span> is -intentional. Under CWA, the truth of the statements is subject to -explicitally stating them.</p> - - - - -<p>For this reason, NRL does not assume an <span style="font-style: italic;">Open World View</span> -and although NRL imposes no semantics on basic -graphs, NRL -semantics are CWA. Semantics are imposed on graphs through Graph Views -and Semantic Views as -introduced in [<a href="#4._Graph_Views_Extensions">Section -4</a>]. Therefore <span style="font-style: italic;">Open -World Views</span> -can be realized as well by applying an OWA view to a -named -graph. On the Semantic Desktop in particular we assume closed-world -semantics -as it focuses mainly on personal data. While most people find it -difficult to understand the logical meaning and potential inferences -statements of the open-world assumption, the closed-world assumption is -easier to understand for an average desktop user. </p> - - - - -</div> - - - - -<div style="width: 909px;"> -<h2><a class="mozTocH2" name="mozTocId154049"></a><a name="2._Representing_Domain_Knowledge:_RDFS"></a>2. -Representing Domain Knowledge: RDF(S) and NRL Extensions to RDF(S)</h2> - - - - -<p style="text-align: justify; width: 900px;">The NRL -Vocabulary is an -application of the [<a href="#References">Resource -Description Framework</a>] (RDF) and the associated [<a href="#References">RDF -Schema</a>] (RDFS). The NRL vocabulary -therefore implicitly includes elements from the RDF/RDFS vocabularies. -Consequently the specifications for RDF [<a href="#References">RDF -Specification</a>] and RDFS should be regarded as part of this -specification document. However, the NRL vocabulary defines some <a href="#2.3._Recommendations"> -recommendations</a> on the use of RDF/RDFS elements. When using -RDF/S constructs within the NRL context, these recommendations need -to be respected if the generated data is to be valid NRL data (see -discussion in [<a href="#1.2">1.2</a>] -regarding -valid and legal NRL). In practice this means that when RDF/S constructs -are used together with NRL elements (or any of their instances) one -should strictly abide by the RDF/S specifications and any -recommendations stated in this document.<br /> - - - - -<br /> - - - - -The rest of Section 2 is divided as follows. Summary tables of the -imported RDF/RDFS elements are provided, followed by specifications of -any restrictions or recommendations placed when importing into NRL.</p> - - - - -<h3><a class="mozTocH3" name="mozTocId866477"></a><a name="2.1_Resource_Description_Framework_RDF"></a>2.1 -Resource Description -Framework -(RDF) Elements</h3> - - - - -<p style="text-align: justify; width: 900px;">The -following are the -elements defined in RDF and implicitly -forming part of the NRL. Their summary tables are categorized into -Classes, Properties and other elements. The class summary table states -the class name and the class’s parent class. The property -summary table states the property name and the applicable domain and -range. The other elements table states the element name and the element -type. The tables also denote whether the elements have been imported as -is, or if extensions or restrictions apply when used in the NEPOMUK -context. These extensions and restrictions are specified in [<a href="#2.3._Recommendations">2.3</a>]</p> - - - - -<h4 style="text-align: justify;"><a class="mozTocH4" name="mozTocId302034"></a><a name="2.1.1_Classes"></a>2.1.1 -Classes</h4> - - - - -<table style="width: 100%;" id="table27" border="1"> - - - - - <tbody> - - - - - <tr> - - - - - <td style="width: 199px;"><i>Class</i></td> - - - - - <td style="width: 521px;"><i>Superclass</i></td> - - - - - <td style="width: 183px;"><i>Notes</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 199px;">rdf:Property</td> - - - - - <td style="width: 521px;">rdfs:Resource</td> - - - - - <td style="width: 183px;">No</td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 199px;">rdf:Statement</td> - - - - - <td style="width: 521px;">rdfs:Resource</td> - - - - - <td style="width: 183px;">No</td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 199px;">rdf:XMLLiteral*</td> - - - - - <td style="width: 521px;">rdfs:Literal</td> - - - - - <td style="width: 183px;">No</td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 199px;">rdf:Bag</td> - - - - - <td style="width: 521px;">rdfs:Container</td> - - - - - <td style="width: 183px;"><a href="#2.3.3_Grouping_resources">Yes</a></td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 199px;">rdf:Seq</td> - - - - - <td style="width: 521px;">rdfs:Container</td> - - - - - <td style="width: 183px;"><a href="#2.3.3_Grouping_resources">Yes</a></td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 199px;">rdf:Alt</td> - - - - - <td style="width: 521px;">rdfs:Container</td> - - - - - <td style="width: 183px;"><a href="#2.3.3_Grouping_resources">Yes</a></td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 199px;">rdf:List</td> - - - - - <td style="width: 521px;">rdfs:Resource</td> - - - - - <td style="width: 183px;">No</td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<p>*rdf:XMLLiteral is also an instance of rdfs:Datatype (see <a href="#2.1.3_Other_Vocabulary"> -Other Vocabulary</a>)</p> - - - - -<h4><a class="mozTocH4" name="mozTocId861838"></a><a name="2.1.2_Properties"></a>2.1.2 -Properties</h4> - - - - -<table style="width: 100%;" id="table28" border="1"> - - - - - <tbody> - - - - - <tr> - - - - - <td style="width: 193px;"><i>Property</i></td> - - - - - <td style="width: 241px;"><i>Domain</i></td> - - - - - <td style="width: 273px;"><i>Range</i></td> - - - - - <td style="width: 183px;"><i>Notes</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 193px;">rdf:type</td> - - - - - <td style="width: 241px;">rdfs:Resource</td> - - - - - <td style="width: 273px;">rdfs:Class</td> - - - - - <td style="width: 183px;">No</td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 193px;">rdf:subject</td> - - - - - <td style="width: 241px;">rdf:Statement</td> - - - - - <td style="width: 273px;">rdfs:Resource</td> - - - - - <td style="width: 183px;">No</td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 193px;">rdf:predicate</td> - - - - - <td style="width: 241px;">rdf:Statement</td> - - - - - <td style="width: 273px;">rdfs:Resource</td> - - - - - <td style="width: 183px;">No</td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 193px;">rdf:object</td> - - - - - <td style="width: 241px;">rdf:Statement</td> - - - - - <td style="width: 273px;">rdfs:Resource</td> - - - - - <td style="width: 183px;">No</td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 193px;">rdf:value</td> - - - - - <td style="width: 241px;">rdfs:Resource</td> - - - - - <td style="width: 273px;">rdfs:Resource</td> - - - - - <td style="width: 183px;">No</td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 193px;">rdf:first</td> - - - - - <td style="width: 241px;">rdf:List</td> - - - - - <td style="width: 273px;">rdfs:Resource</td> - - - - - <td style="width: 183px;">No</td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 193px;">rdf:rest</td> - - - - - <td style="width: 241px;">rdf:List</td> - - - - - <td style="width: 273px;">rdf:List</td> - - - - - <td style="width: 183px;">No</td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<h4><a class="mozTocH4" name="mozTocId355985"></a><a name="2.1.3_Other_Vocabulary"></a>2.1.3 -Other -Vocabulary</h4> - - - - -<table style="width: 100%;" id="table29" border="1"> - - - - - <tbody> - - - - - <tr> - - - - - <td style="width: 193px;"><i>Name</i></td> - - - - - <td style="width: 519px;"><i>Type</i></td> - - - - - <td style="width: 184px;"><i>Notes</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 193px;">rdf:nil</td> - - - - - <td style="width: 519px;">rdfs:List</td> - - - - - <td style="width: 184px;">No</td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 193px;">rdf:XMLLiteral</td> - - - - - <td style="width: 519px;">rdfs:Datatype</td> - - - - - <td style="width: 184px;">No</td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<h3><a class="mozTocH3" name="mozTocId794884"></a><a name="2.2._RDF_Schema_RDFS_Elements"></a>2.2. -RDF Schema (RDFS) -Elements</h3> - - - - -<p style="text-align: justify;">The following are the -elements defined in RDFS and -implicitly -forming part of the NRL. Their summary tables are categorized into -Classes and Properties. The class summary table states the class name -and the class’s parent class. The property summary table -states the property name and the applicable domain and range. The -tables also denote whether the elements have been imported as is, or if -extensions apply when used in the NRL context. These extensions are -specified in [<a href="#2.3._Recommendations">2.3</a>]</p> - - - - -<h4><a class="mozTocH4" name="mozTocId679335"></a><a name="2.2.1_Classes"></a>2.2.1 Classes</h4> - - - - -<table style="width: 100%;" id="table30" border="1"> - - - - - <tbody> - - - - - <tr> - - - - - <td style="width: 253px;"><i>Class</i></td> - - - - - <td style="width: 460px;"><i>Superclass</i></td> - - - - - <td style="width: 183px;"><i>Notes</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 253px;">rdfs:Resource</td> - - - - - <td style="width: 460px;">rdfs:Resource</td> - - - - - <td style="width: 183px;">No</td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 253px;">rdfs:Class</td> - - - - - <td style="width: 460px;">rdfs:Resource</td> - - - - - <td style="width: 183px;">No</td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 253px;">rdfs:Datatype</td> - - - - - <td style="width: 460px;">rdfs:Class</td> - - - - - <td style="width: 183px;">No</td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 253px;">rdfs:Container</td> - - - - - <td style="width: 460px;">rdfs:Resource</td> - - - - - <td style="width: 183px;"><a href="#2.3.3_Grouping_resources">Yes</a></td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 253px;">rdfs:Literal</td> - - - - - <td style="width: 460px;">rdfs:Resource</td> - - - - - <td style="width: 183px;">No</td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 253px;">rdfs:ContainerMembershipProperty</td> - - - - - <td style="width: 460px;">rdf:Property</td> - - - - - <td style="width: 183px;"><a href="#2.3.3_Grouping_resources">Yes</a></td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<h4><a class="mozTocH4" name="mozTocId295955"></a><a name="2.2.2_Properties"></a>2.2.2 -Properties</h4> - - - - -<table style="width: 100%;" id="table31" border="1"> - - - - - <tbody> - - - - - <tr> - - - - - <td style="width: 312px;"><i>Property</i></td> - - - - - <td style="width: 326px;"><i>Domain</i></td> - - - - - <td style="width: 258px;"><i>Range</i></td> - - - - - <td style="width: 250px;"><i>Notes</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 312px;">rdfs:domain</td> - - - - - <td style="width: 326px;">rdf:Property</td> - - - - - <td style="width: 258px;">rdfs:Class</td> - - - - - <td style="width: 250px;"><a href="#2.3.1_rdfs:domain_rdfs:range">Yes</a></td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 312px;">rdfs:range</td> - - - - - <td style="width: 326px;">rdf:Property</td> - - - - - <td style="width: 258px;">rdfs:Class</td> - - - - - <td style="width: 250px;"><a href="#2.3.1_rdfs:domain_rdfs:range">Yes</a></td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 312px;">rdfs:subClassOf</td> - - - - - <td style="width: 326px;">rdfs:Class</td> - - - - - <td style="width: 258px;">rdfs:Class</td> - - - - - <td style="width: 250px;">No</td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 312px;">rdfs:subPropertyOf</td> - - - - - <td style="width: 326px;">rdf:Property</td> - - - - - <td style="width: 258px;">rdf:Property</td> - - - - - <td style="width: 250px;">No</td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 312px;">rdfs:member</td> - - - - - <td style="width: 326px;">rdfs:Resource</td> - - - - - <td style="width: 258px;">rdfs:Resource</td> - - - - - <td style="width: 250px;"><a href="#2.3.3_Grouping_resources">Yes</a></td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 312px;">rdfs:isDefinedBy*</td> - - - - - <td style="width: 326px;">rdfs:Resource</td> - - - - - <td style="width: 258px;">rdfs:Resource</td> - - - - - <td style="width: 250px;"><a href="#2.3.4_rdfs:isDefinedBy">Yes</a></td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 312px;" height="24">rdfs:label</td> - - - - - <td style="width: 326px;" height="24">rdfs:Resource</td> - - - - - <td style="width: 258px;" height="24">rdfs:Literal</td> - - - - - <td style="width: 250px;" height="24">No</td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 312px;">rdfs:comment</td> - - - - - <td style="width: 326px;">rdfs:Resource</td> - - - - - <td style="width: 258px;">rdfs:Literal</td> - - - - - <td style="width: 250px;">No</td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 312px;">rdfs:seeAlso</td> - - - - - <td style="width: 326px;">rdfs:Resource</td> - - - - - <td style="width: 258px;">rdfs:Resource</td> - - - - - <td style="width: 250px;">No</td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<p>*rdfs:isDefinedBy is a sub property of rdfs:seeAlso</p> - - - - -</div> - - - - -<h3><a class="mozTocH3" name="mozTocId589481"></a><a name="2.3._Recommendations_for_and_against_the"></a>2.3. -Recommendations for and -against the use of RDF/S elements</h3> - - - - -<p>As discussed earlier [<a href="#1.2">Section -1.2</a>] although -any legal RDF is also legal NRL, it is not necessarily valid NRL. In -order for NRL to be valid, these recommendations must be strictly -adhered to.</p> - - - - -<h4><a class="mozTocH4" name="mozTocId522073"></a><a name="2.3.1_rdfs:domain_rdfs:range"></a>2.3.1 -rdfs:domain, rdfs:range</h4> - - - - -<p style="text-align: justify;"><big><span style="font-size: 12pt;">The -fact that NRL does not assume open-world has an -impact on the way some constructs should be used. This is especially -true for -the rdfs:domain and the rdfs:range elements. In an open-world scenario, -when -using a property to relate two resources, one is implicitly casting the -type of -those resources to the types specified in the property’s -domain and range -definition. In other words the use of a property evokes additional -implicit -statements about the types of the objects being related, even if these -types -are different than the types that have been predefined for the objects, -if at -all. In a closed-world scenario as on the semantic -desktop this is not possible since in order to -relate -two resources, their types must fit the expected domain and range in -the first -place. This also means that untyped resources cannot be related. -Failure to do -so will generate legal yet invalid NRL data on the semantic desktop. -This recommendation has a -major bearing -on the validity of logical inference mechanisms in place within NRL and -therefore must be strictly adhered to.</span></big><br /> - - - - -</p> - - - - -<span style="font-style: italic;"><span style="font-weight: bold;">Recommendation: </span></span><i>The -domain and range constraints for -properties must be strictly adhered to. Untyped resources cannot be -related -through a property, since the types of the related resources must -explicitly -satisfy the constraints set by rdfs:domain and rdfs:range given NRL is -not OWA.<br /> - - - - -</i><br /> - - - - -<i>Examples</i> -<p style="text-align: justify;">In these examples and -the ones that follow throughout the -document, we use the example namespace for user-generated data <span style="font-family: monospace;">http://mydesktop.org/mydesktop#</span>. -The example namespace abbreviation can be defined as follows. To -improve the readability of examples, the user namespace abbreviation is -sometimes excluded. In these cases, the elements are given in italics.</p> - - - - -<table style="text-align: left; width: 100%;" border="1" cellpadding="2" cellspacing="2"> - - - - - <tbody> - - - - - <tr> - - - - - <td><span style="font-family: monospace;"> @prefix -rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> @prefix -rdfs: <http://www.w3.org/2000/01/rdf-schema#> .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> @prefix -nrl: -<http://www.semanticdesktop.org/ontology/yyyy/mm/dd/nrl#> -.</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> @prefix -voc: <http://www.semanticdesktop.org/ontology/desktop#> .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> ...</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> @prefix -desktop: <http://mydesktop.org/mydesktop#> .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> ...</span></td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<br /> - - - - -[1] Within the Ontology <span style="font-style: italic;">Desktop</span> -the -property voc:depicts is assigned a domain of voc:ImageFile and a range -of voc:Person.<br /> - - - - -<br /> - - - - -[2] desktop:Myself is defined as an instance of voc:Person.<br /> - - - - -<br /> - - - - -[3] desktop:MyFriend is defined as an instance of voc:Friend.<br /> - - - - -<br /> - - - - -[4] desktop:PassportPhoto is defined as an instance of voc:ImageFile. -It is related to desktop:Myself through the voc:depicts property. This -is valid usage of the rdfs:domain and -rdfs:range as defined in [1] and is valid NRL data, since the types of -both resources being related have been stated and they fit the domain -and range constraints.<br /> - - - - -<br /> - - - - -[5] -desktop:Friend20060613 is defined -as an instance of voc:ImageFile. It is related to desktop:MyFriend -through the voc:depicts property. It is nowhere stated that the class -voc:Friend is a subclass of voc:Person. This is legal, but not -valid usage of the rdfs:domain and -rdfs:range as defined in [1]. Given the closed-world -assumption, -it cannot be determined whether the statement 'desktop:MyFriend is -voc:Person' is true. Note that if voc:Friend was defined as a -subclass of voc:Person, the statement would become true -and -therefore the NRL data would be both legal and valid.<br /> - - - - -<br style="font-family: monospace;" /> - - - - -<table style="text-align: left; width: 100%;" border="1" cellpadding="2" cellspacing="2"> - - - - - <tbody> - - - - - <tr> - - - - - <td><span style="font-family: monospace;">[1] -:o1 {</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ...</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - voc:depicts rdf:type rdf:Property ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdf:domain voc:ImageFile ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdf:range voc:Person ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdfs:subClassOf voc:Person . }</span><br style="font-family: monospace;" /> - - - - - <br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - :ib1 { </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ...</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[2] -desktop:Myself rdf:type voc:Person . </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[3] -desktop:MyFriend rdf:type voc:Friend . </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[4] -desktop:PassportPhoto rdf:type voc:ImageFile ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - voc:depicts -desktop:Myself .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[5] -desktop:Friend20060613 rdf:type voc:ImageFile ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - - voc:depicts desktop:MyFriend . } </span></td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<br /> - - - - -<h4><a class="mozTocH4" name="mozTocId332366"></a><a name="2.3.2_Blank_Nodes"></a>2.3.2 -Blank Nodes</h4> - - - - -<p style="text-align: justify;">The use of blank nodes -in conjunction with NRL elements and -their instances is strongly discouraged. Blank nodes are semantically -difficult to handle and as a result it is difficult to implement them -correctly. </p> - - - - -<div style="text-align: justify;"><i><span style="font-weight: bold;">Recommendation:</span> The -use of blank nodes is strongly -discouraged. Data containing blank nodes is legal but not valid NRL -data.<br /> - - - - -</i> -<h4><a class="mozTocH4" name="mozTocId397156"></a><a name="2.3.3_Grouping_resources"></a>2.3.3 -Collections -and Containers</h4> - - - - -<p>Container classes are -deprecated because the semantics of -containers are not clear and they are also difficult to handle. The -sole use of either containers or collections is sufficient to model -grouped resources. Since the semantics of collections are clearer, the -use of containers is discouraged in favour of collections.</p> - - - - -<ol> - - - - - <li>rdf:Bag is a -container class whose use is discouraged.</li> - - - - - <li>rdf:Alt is a -container class whose use is discouraged.</li> - - - - - <li style="text-align: justify;">rdf:Seq is a -container class whose use is discouraged.</li> - - - - - <li style="text-align: justify;">rdfs:Container is the -superclass of rdf:Bag, rdf:Alt and -rdf:Seq, and is not applicable to any other RDF/S or NRL element.</li> - - - - - <li style="text-align: justify;">rdfs:ContainerMembershipProperty -is used to indicate the -membership of rdf:Bag, rdf:Alt and rdf:Seq, and is not applicable to -any other RDF/S or NRL element.</li> - - - - - <li style="text-align: justify;">rdfs:member is a -super property of the container -membership -properties, and is not applicable to any other RDF/S or NRL element.</li> - - - - -</ol> - - - - -<span style="font-weight: bold; font-style: italic;">Recommendation:</span><span style="font-style: italic;"> -The use elements numbered [1] -through -[6] is strongly discouraged. <br /> - - - - -</span> -<p>Although the use of -container classes and properties is -discouraged, resources can still be grouped using [<a href="http://www.w3.org/TR/rdf-schema/#ch_collectionvocab">RDFS -Collections</a>] constructs.</p> - - - - -</div> - - - - -<ol> - - - - - <li>rdf:List is a class that can be used to build -descriptions -of collections. A collection typically is composed of one or more lists.</li> - - - - - <li>rdf:first is a property that relates a list to its first -element.</li> - - - - - <li>rdf:rest is a property that relates a list to the rest of -the elements excluding the first element. The rest of the elements are -in the form of another list.</li> - - - - - <li>rdf:nil is a property that can be used to create an empty -list. This is usually the last list in a collection.</li> - - - - -</ol> - - - - -<i><span style="font-weight: bold;">Recommendation:</span> -The combined use of elements -numbered -[1] through [4] is encouraged as an alternative to container elements<br /> - - - - -</i> -<h4><a class="mozTocH4" name="mozTocId220340"></a><a name="2.3.4_rdfs:isDefinedBy"></a>2.3.4 -rdfs:isDefinedBy</h4> - - - - -<p style="text-align: justify;">The semantics of this -element is unclear and therefore it is -discouraged. The definition vaguely -allows the use of this property to relate any two resources.</p> - - - - -<i><span style="font-weight: bold;">Recommendation:</span> -The use of rdfs:isDefinedBy is -strongly discouraged. Data containing statements using this property is -legal but not valid NRL data.</i> -<h4><a class="mozTocH4" name="mozTocId361071"></a><a name="2.3.5_Reification"></a>2.3.5 -Reification</h4> - - - - -<p style="background-color: rgb(255, 255, 255);">The -named -graphs paradigm provides all -the functionality required to be able to state things about other -statements. Consequently, the idea of reification within the NRL -context is redundant. </p> - - - - -<span style="background-color: rgb(255, 255, 255);"></span><span style="font-style: italic; background-color: rgb(255, 255, 255);"><span style="font-weight: bold;">Recommendation:</span> -The use of reification is strongly discouraged.</span><span style="background-color: rgb(255, 255, 255);"> -</span><br /> - - - - -<h3><a class="mozTocH3" name="mozTocId932814"></a><a name="2.4._Constraint_Extensions"></a>2.4. -Constraint Extensions</h3> - - - - -<p>This -section -presents extensions used to make statements -about constraints on the use of properties in NRL data. These -extensions provide further functionalities to the basic -constraints provided by RDFS, namely [<a href="http://www.w3.org/TR/rdf-schema/#ch_domain">rdfs:domain</a>] -and [<a href="http://www.w3.org/TR/rdf-schema/#ch_range">rdfs:range</a>]. -The latter two constraints place a limitation on the class -type of the resources that a property can relate (<span style="font-style: italic;">class type</span> <span style="font-style: italic;">constraints</span>).<span style="font-style: italic;"> </span>The NRL -constraint extensions in turn place a limitation on the amount -of values that a property can take (<span style="font-style: italic;">range -cardinality constraints</span>) and on actual pairs of -resources that the property should or should -not, through inference, relate (<span style="font-style: italic;">resource -relation constraints</span>). -These three categories are -summarized in [<a href="#Table_1">Table 1</a>]. -Similarly -to RDFS, NRL provides a mechanism for describing these constraints, but -does -not say whether or how an application must process the constraint -information. In particular, in the Social Semantic Desktop scenario, -different applications -will use -the -constraints in different ways. NRL Validators will be expected to check -for errors, -interactive editors to suggest legal values, and reasoners to -perform inference and inconsistency checks.</p> - - - - -<table style="text-align: left; width: 100%; height: 228px;" border="1" cellpadding="2" cellspacing="2"> - - - - - <tbody> - - - - - <tr> - - - - - <td style="font-style: italic; width: 220px;">Class -Type -Constraints</td> - - - - - <th colspan="1" rowspan="8" style="width: 87px;"></th> - - - - - <td style="font-style: italic; width: 231px;">Range -Cardinality -Constraints</td> - - - - - <td colspan="1" rowspan="8" style="width: 94px;"></td> - - - - - <td style="font-style: italic; width: 244px;">Resource -Relation Constraints</td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 220px;">rdfs:domain</td> - - - - - <td style="width: 231px;"><a href="#2.4.7._nrl:cardinality">nrl:cardinality</a></td> - - - - - <td style="width: 244px;"><a href="#2.4.1._nrl:TransitiveProperty">nrl:TransitiveProperty</a></td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 220px;">rdfs:range</td> - - - - - <td style="width: 231px;"><a href="#2.4.8._nrl:minCardinality">nrl:minCardinality</a></td> - - - - - <td style="width: 244px;"><a href="#2.4.2._nrl:SymmetricProperty">nrl:SymmetricProperty</a></td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 220px;"><br /> - - - - - </td> - - - - - <td style="width: 231px;"><a href="#2.4.9._nrl:maxCardinality">nrl:maxCardinality</a></td> - - - - - <td style="width: 244px;"><a href="#2.4.3._nrl:AsymmetricProperty">nrl:AsymmetricProperty</a></td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 220px;"><br /> - - - - - </td> - - - - - <td style="width: 231px;"><br /> - - - - - </td> - - - - - <td style="width: 244px;"><a href="#2.4.4._nrl:ReflexiveProperty">nrl:ReflexiveProperty</a></td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 220px;"><br /> - - - - - </td> - - - - - <td style="width: 231px;"><br /> - - - - - </td> - - - - - <td style="width: 244px;"><a href="#2.4.10._nrl:inverseProperty">nrl:inverseProperty</a></td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 220px;"><br /> - - - - - </td> - - - - - <td style="width: 231px;"><br /> - - - - - </td> - - - - - <td style="width: 244px;"><a href="#2.4.5._nrl:FunctionalProperty">nrl:FunctionalProperty</a></td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 220px;"><br /> - - - - - </td> - - - - - <td style="width: 231px;"><br /> - - - - - </td> - - - - - <td style="width: 244px;"><a href="#2.4.6._nrl:InverseFunctionalProperty">nrl:InverseFunctionalProperty</a></td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<div style="margin-left: 40px; text-align: center;"><a name="Table_1"></a>Table -1: NRL Constraints </div> - - - - -<div style="text-align: justify;"> -<p>It -should be noted, that the -recommendation given for the RDFS constraints in [<a href="#2.3.1_rdfs:domain_rdfs:range">2.3.1.</a>] -is extended to the NRL constraint extensions. <span style="font-size: 12pt;">Given -a possible closed-world view, in order to -generate valid NRL data a user (human or machine) should check, prior -to using -a property, whether the resources are indeed valid candidates which -satisfy the -constraints.</span></p> - - - - -<p>The following are the classes ([<a href="#2.4.1._nrl:TransitiveProperty">2.4.1.</a>] -- [<a href="#2.4.6._nrl:InverseFunctionalProperty">2.4.6.</a>]) -and properties ([<a href="#2.4.7._nrl:cardinality">2.4.7.</a>] -- [<a href="#2.4.10._nrl:inverseProperty">2.4.10.</a>]) -provided in NRL as -constraint extensions to RDF/S. </p> - - - - -<h4><a class="mozTocH4" name="mozTocId770989"></a><a name="2.4.1._nrl:TransitiveProperty"></a>2.4.1. -nrl:TransitiveProperty</h4> - - - - -</div> - - - - -<p style="text-align: justify;">Properties -may be defined -to -be transitive. If a transitive -property relates resource X to resource Y as well as Y to resource Z, -then it follows that the property also relates X to Z. Semantic views -can realize these declarative semantics by generating -entailment -triples. This class is similar -to [<a href="http://www.w3.org/TR/owl-ref/#TransitiveProperty-def">owl:TransitiveProperty</a>].</p> - - - - -<span style="font-style: italic; font-weight: bold;">Note:</span> -Transitive properties and their superproperties should -not be assigned a maximum cardinality restriction of one. This would -contradict the fact that the resource X described above can be -transitively related to both Y and Z. -<br /> - - - - -<br /> - - - - -<span style="font-style: italic; font-weight: bold;">Note:</span> -Transitive properties should not be defined as [<a href="#2.4.5._nrl:FunctionalProperty">nrl:FunctionalProperty</a>] -properties. If a -transitive functional property relates X to Y, then X cannot be related -to other resources by that same property. Thus transitivity cannot -hold. <br /> - - - - -<br /> - - - - -<span style="font-style: italic; font-weight: bold;">Note:</span> -Transitive properties should not be defined as [<a href="#2.4.6._nrl:InverseFunctionalProperty">nrl:InverseFunctionalProperty</a>] -properties. If a -transitive inverse functional property relates X to Y, then Y cannot be -related to other resources by that same property. Thus transitivity -cannot hold. -<br /> - - - - -<i><br /> - - - - -Example</i> -<br /> - - - - -<br /> - - - - -[1] -voc:containsFolder -is defined as an instance of -rdf:Property, applicable to instances of voc:Folder and taking -instances of voc:Folder as a values. voc:containsFolder is also -defined to be an instance of [<a href="#2.4.1._nrl:TransitiveProperty">nrl:TransitiveProperty</a>]. -<br /> - - - - -<br /> - - - - -[2] -desktop:MyPapers is -defined to be an instance of class voc:Folder. Another voc:Folder, -desktop:PublishedPapers is -related to desktop:MyPapers by the transitive property -voc:containsFolder. -<br /> - - - - -<br /> - - - - -[3] -desktop:PublishedPapers -is defined to be an instance of -class voc:Folder. Another voc:Folder, desktop:ShortPapers is -related to desktop:PublishedPapers by the transitive property -voc:containsFolder. -<br /> - - - - -<p>Since <i>containsFolder</i> -is a transitive -property, a reasoner can easily deduce that since <i>MyPapers - -containsFolder - PublishedPapers</i> and <i>PublishedPapers -- containsFolder - ShortPapers</i>, then <i>MyPapers - -containsFolder - ShortPapers</i> as well.</p> - - - - -<table style="text-align: left; width: 100%;" border="1" cellpadding="2" cellspacing="2"> - - - - - <tbody> - - - - - <tr> - - - - - <td><span style="font-family: monospace;"> - :o1 {</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ...</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - voc:containsFolder rdf:type rdf:Property ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdf:domain -voc:Folder ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdf:range -voc:Folder ; </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[1] - - rdf:type nrl:TransitiveProperty . }</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - :ib1 { </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ...</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - desktop:MyPapers rdf:type voc:Folder ; </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[2] - - voc:containsFolder desktop:PublishedPapers .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[3] -desktop:PublishedPapers rdf:type voc:Folder ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - - voc:containsFolder desktop:ShortPapers . }</span></td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<br /> - - - - -<h4><a class="mozTocH4" name="mozTocId779070"></a><a name="2.4.2._nrl:SymmetricProperty"></a>2.4.2. -nrl:SymmetricProperty</h4> - - - - -<p>Properties can be defined -to -be symmetric. If a symmetric -property relates resource X to resource Y, then it follows that Y is -related to X by the same property. Examples follow [<a href="#2.4.4._nrl:ReflexiveProperty">5.1.4.</a>]. This -class is similar to [<a href="http://www.w3.org/TR/owl-ref/#SymmetricProperty-def">owl:SymmetricProperty</a>].</p> - - - - -<h4><a class="mozTocH4" name="mozTocId832124"></a><a name="2.4.3._nrl:AsymmetricProperty"></a>2.4.3. -nrl:AsymmetricProperty</h4> - - - - -<p>Properties can also be -defined to be asymmetric. Then if -asymmetric property relates X to Y, then Y cannot be related to X by -the same property.</p> - - - - -<h4><a class="mozTocH4" name="mozTocId890283"></a><a name="2.4.4._nrl:ReflexiveProperty"></a>2.4.4. -nrl:ReflexiveProperty</h4> - - - - -<p style="text-align: justify;">Properties -can be defined -to -be reflexive. This would -restrict -the use of this property to relate a resource to itself. Hence, -reflexive properties can only relate resource X to itself.</p> - - - - -<i>Examples</i> -<br /> - - - - -<br /> - - - - -[1] -voc:relatedTopic -is -defined as an instance of -rdf:Property, applicable to instances of <span style="font-family: monospace;">voc</span>:Folder and -taking -instances of voc:Folder as values.<i> relatedTopic</i> -is defined to be an instance of [<a href="#2.4.2._nrl:SymmetricProperty">nrl:SymmetricProperty</a>]. -<br /> - - - - -<br /> - - - - -[2] -voc:hasTopic -is -defined as an instance of -rdf:Property, applicable to instances of <span style="font-family: monospace;">voc</span>:Folder and -taking -instances of voc:Topic as values.<i> hasTopic</i> -is defined to be an instance of [<a href="#2.4.3._nrl:AsymmetricProperty">nrl:AsymmetricProperty</a>]. -<br /> - - - - -<br /> - - - - -[3] -desktop:Publications -is -defined to be an instance of -class voc:Topic. Another voc:Topic, desktop:Research is defined to be -a voc:relatedTopic of desktop:Publications. -<br /> - - - - -Since <i>relatedTopic</i> -is a symmetric -property, it can be inferred that <i>Publications</i> is a -<i>relatedTopic</i> of <i>Research</i>. -<br /> - - - - -<br /> - - - - -[4] -desktop:PublishedPapers -is defined to be an instance of -class voc:Folder. desktop:PublishedPapers is also stated to have -topic desktop:Publications. -<p style="text-align: justify;">Since <i>hasTopic</i> -is an asymmetric -property, -a reasoner would know that it is not possible to say that the<i> </i>topic -<i>Publications</i> has as topic the<i> </i>folder<i> -PublishedPapers</i>.</p> - - - - -<table style="text-align: left; width: 100%;" border="1" cellpadding="2" cellspacing="2"> - - - - - <tbody> - - - - - <tr> - - - - - <td> <span style="font-family: monospace;"> :o1 {</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ...</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - voc:relatedTopic rdf:type rdf:Property ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdf:domain voc:Topic ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdf:range voc:Topic ; </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[1] - - rdf:type nrl:SymmetricProperty . </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - voc:hasTopic rdf:type rdf:Property ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdf:domain voc:Folder ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdf:range voc:Topic ; </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[2] - - rdf:type nrl:AsymmetricProperty . }</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - :ib1 { </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ...</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[3] -desktop:Publications rdf:type voc:Topic ; </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - -voc:relatedTopic desktop:Research .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[4] -desktop:PublishedPapers rdf:type voc:Folder ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - -voc:hasTopic desktop:Publications . }</span></td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<br /> - - - - -<h4><a class="mozTocH4" name="mozTocId687239"></a><a name="2.4.5._nrl:FunctionalProperty"></a>2.4.5. -nrl:FunctionalProperty</h4> - - - - -<p style="text-align: justify;">Properties -can be defined -to -be functional. This translates -into the property having a minimum cardinality of zero and a maximum -cardinality of one <span style="font-style: italic;">for -each</span> unique resource that is applied as its domain. -Therefore, if a functional property relates -resource X to resource Y, then it means that X cannot be forward -related to other resources by that same property. In simpler words, the -value of such a property for resource X, if stated, is unique. Example -follows [<a href="#2.4.6._nrl:InverseFunctionalProperty">3.1.13</a>]. This -class is similar to [<a href="http://www.w3.org/TR/owl-ref/#FunctionalProperty-def">owl:FunctionalProperty</a>].</p> - - - - -<h4><a class="mozTocH4" name="mozTocId86301"></a><a name="2.4.6._nrl:InverseFunctionalProperty"></a>2.4.6. -nrl:InverseFunctionalProperty</h4> - - - - -<p>A property can also be -defined to be inverse functional. -Such -a property implies that the inverse of the property is functional. This -does not automatically mean that an inverse property of the property in -question is actually defined using [<a href="#2.4.10._nrl:inverseProperty">nrl:inverseProperty</a>]. -This translates -into the property having a minimum cardinality of zero and a maximum -cardinality of one <span style="font-style: italic;">for -each</span> unique resource that is applied as its range. -Therefore, if such a property relates resource X to resource -Y, then it means that Y cannot be backward related to other resources -using that same property. In other words, if Y is defined as the -property value for one resource, then it cannot be defined as the -property value for another resource. This class is similar -to [<a href="http://www.w3.org/TR/owl-ref/#InverseFunctionalProperty-def">owl:InverseFunctionalProperty</a>].</p> - - - - -<i>Examples</i><br /> - - - - -<br /> - - - - -[1] -voc:user is -defined -as an instance of rdf:Property, -applicable to instances of voc:Desktop and taking instances of -voc:Person as a values. desktop:user is defined to be an instance -of [<a href="#2.4.5._nrl:FunctionalProperty">nrl:FunctionalProperty</a>]. -<br /> - - - - -<br /> - - - - -[2] -voc:email is -defined -as an instance of rdf:Property, -applicable to instances of voc:Person and taking string datatypes -as values. voc:email is defined to be an instance of -[<a href="#2.4.6._nrl:InverseFunctionalProperty">nrl:InverseFunctionalProperty</a>]. -<br /> - - - - -<br /> - - - - -[3] -desktop:MyPersonalDesktop is defined to be an instance -of -class voc:Desktop. It is related to <i>Person</i> -desktop:MyUserName by the property voc:user. -<p style="text-align: justify;">Since <i>user</i> -is a functional property, it -can be concluded that this instance of <i>Desktop</i> has -only that unique particular instance of <i>Person</i> as <i>user</i>. -No other instances of <i>Person</i> can be defined as the <i>user</i> -of this <i>Desktop</i>. Under the closed-world -assumption this would generate warning over conflicting -data. </p> - - - - -[4] -desktop:MyUserName is -defined to be an instance of class voc:Person with a voc:email value of -<i>user.name@host.com.</i> -<p style="text-align: justify;">Since <i>email</i> -is an inverse -functional property, it follows that <i>user.name@host.com -</i>cannot belong to other instances of <i>Person</i>. Doing -so might result in conflicting data due to NRL's closed-world -assumption.</p> - - - - -<table style="text-align: left; width: 100%;" border="1" cellpadding="2" cellspacing="2"> - - - - - <tbody> - - - - - <tr> - - - - - <td><span style="font-family: monospace;"> - :o1 {</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ...</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - voc:user rdf:type rdf:Property ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - -rdf:domain voc:Desktop ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdf:range voc:Person ; </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[1] - rdf:type -nrl:FunctionalProperty . </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - voc:email rdf:type rdf:Property ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdf:domain voc:Person ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdf:range -<http://www.w3.org/2001/XMLSchema#string> ; </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[2] - - rdf:type nrl:InverseFunctionalProperty . }</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - :ib1 { </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ...</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[3] -desktop:MyPersonalDesktop rdf:type voc:Desktop ; </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - - voc:user desktop:MyUsername .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[4] -desktop:MyUserName rdf:type voc:Person ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - voc:email -"user.name@host.com" . }</span></td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<br /> - - - - -<h4><a class="mozTocH4" name="mozTocId97363"></a><a name="2.4.7._nrl:cardinality"></a>2.4.7. -nrl:cardinality</h4> - - - - -This property is a -cardinality restriction property. It -can -be -applied to instances of rdf:Property to specify a constraint on the -number <span style="font-style: italic;">n</span> -of values that the property can have <span style="font-style: italic;">for -each</span> unique -resource that is applied as its domain. The value -allowed for this property is a nonNegativeInteger data value from the -XML Schema datatypes. This states that instances of the restricted -property must have exactly <span style="font-style: italic;">n</span> -semantically distinct values. In order to -correctly use the NRL vocabulary, this restriction must be always -strictly respected. This property is similar to [<a href="http://www.w3.org/TR/owl-ref/#cardinality-def">owl:cardinality</a>].<br /> - - - - -<h4><a class="mozTocH4" name="mozTocId435982"></a><a name="2.4.8._nrl:minCardinality"></a>2.4.8. -nrl:minCardinality</h4> - - - - -<p>This property is a -cardinality restriction property. It -can -be -applied to instances of rdf:Property to specify a constraint on the -minimum number <span style="font-style: italic;">n</span> -of values that the property can have for each unique resource -it is applied as its domain. The -value allowed for this property is a nonNegativeInteger data value from -the XML Schema datatypes. This states that instances of the restricted -property must have at least <span style="font-style: italic;">n</span> -(<span style="font-style: italic;">n</span> or more) -semantically distinct values. -In particular, properties with a minimum cardinality of one must have -at least one value to be semantically valid. Properties whose minimum -cardinality constraint is not defined have a default minimum -cardinality of zero. In order to correctly use the NRL vocabulary, this -restriction must be always strictly respected. This property is similar -to the Protégé minimum cardinality property -constraints and to [<a href="http://www.w3.org/TR/owl-ref/#minCardinality-def">owl:minCardinality</a>].</p> - - - - -<h4><a class="mozTocH4" name="mozTocId297991"></a><a name="2.4.9._nrl:maxCardinality"></a>2.4.9. -nrl:maxCardinality</h4> - - - - -<p>This property is a -cardinality restriction property. It -can -be -applied to instances of rdf:Property to specify a constraint on the -maximum number <span style="font-style: italic;">n</span> -of values that the property can have for each unique resource it is -applied as its domain. The -value allowed for this property is a nonNegativeInteger data value from -the XML Schema datatypes. This states that instances of the restricted -property must have at most <span style="font-style: italic;">n</span> -(<span style="font-style: italic;">n</span> or less) -semantically distinct values. -In particular, a property with a maximum cardinality of zero would be -of no use since it should never contain any values. Properties -whose maximum cardinality constraint is not -defined -have a default infinite maximum cardinality. In order to correctly use -the NRL vocabulary, this restriction must be always strictly respected. -This property is similar to the Protégé maximum -cardinality property constraints and to [<a href="http://www.w3.org/TR/owl-ref/#maxCardinality-def">owl:maxCardinality</a>].</p> - - - - -Examples<br /> - - - - -<br /> - - - - -The property -desktop:contactEmail is defined as being -applicable to voc:ContactPerson and to have a value of -voc:EmailAddress. Furthermore a restriction is placed on the -minimum cardinality of the values for this property [1]. The minimum -number of values for this property is one. This means, that all <i>ContactPerson</i> -instances must be assigned at least one <i>EmailAddress</i>.<br /> - - - - -<br /> - - - - -<table style="text-align: left; width: 100%;" border="1" cellpadding="2" cellspacing="2"> - - - - - <tbody> - - - - - <tr> - - - - - <td><span style="font-family: monospace;"> - :o1 {</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ...</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - voc:contactEmail rdf:type rdf:Property ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdf:domain voc:ContactPerson -;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdf:range voc:EmailAddress ; - </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[1] - - nrl:minCardinality "1" . }</span></td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<br /> - - - - -This second example -demonstrates the combinatorial use of -cardinality constraints on properties. The property voc:firstName -is defined as being applicable to voc:ContactPerson and to have a -string datatype value. Two restrictions are placed on the minimum [2] -and maximum [3] cardinality of the values for this property [2]. The -value for both restrictions is set to one. This means, that all <i>ContactPerson</i> -instances must be assigned exactly one <i>firstName</i>.<br /> - - - - -<br /> - - - - -<table style="text-align: left; width: 100%;" border="1" cellpadding="2" cellspacing="2"> - - - - - <tbody> - - - - - <tr> - - - - - <td><span style="font-family: monospace;"> - :o1 {</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ...</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - voc:firstName rdf:type rdf:Property ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdf:domain voc:ContactPerson ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdf:range -<http://www.w3.org/2001/XMLSchema#string> ; </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[2] - -nrl:minCardinality "1" ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[3] - -nrl:maxCardinality "1" . }</span></td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<br /> - - - - -<h4><a class="mozTocH4" name="mozTocId72221"></a><a name="2.4.10._nrl:inverseProperty"></a>2.4.10. -nrl:inverseProperty</h4> - - - - -<p style="text-align: justify;">Properties are mainly -distinguished by their domain and -range. -Some properties are the exact inverse of each others, where the range -and domain of property A are the domain and range of property B -respectively. In order to provide efficient reasoning and query -handling, the NRL requires that such inverse functionality of two -properties is explicitly stated using the [<a href="#2.4.10._nrl:inverseProperty">nrl:inverseProperty</a>]. -Stating -that a new property B is the inverse property of predefined property A -is equivalent to stating that the range of A is the domain of B and the -domain of A is the range of B. This will help enable the logical -inference of some implicit statements from other explicit statements. -If property A and property B are defined to be inverse properties, -stating that resource X is related by property A to resource Y will -evoke the statement that resource Y is related by property B to -resource X. This property is comparable to -Protégé’s inverse property and [<a href="http://www.w3.org/TR/owl-ref/#inverseOf-def">owl:inverseOf</a>].</p> - - - - -<i>Example</i><br /> - - - - -<br /> - - - - -[1] voc:hasFile is -defined as an instance of -rdf:Property, -applicable to instances of voc:Folder and taking instances of voc:File -as a values.<br /> - - - - -<br /> - - - - -[3] voc:inFolder is -likewise defined as an instance of -rdf:Property, applicable to instances of voc:File and taking -instances of voc:Folder as values. The domain of voc:hasFile is -equivalent to the range of voc:inFolder, while the range of voc:hasFile -is equivalent to the domain of voc:inFolder.<br /> - - - - -<br /> - - - - -[2,4] This implicit -inverse relationship is explicitly -stated -in both properties.<br /> - - - - -<table style="text-align: left; width: 100%;" border="1" cellpadding="2" cellspacing="2"> - - - - - <tbody> - - - - - <tr> - - - - - <td><span style="font-family: monospace;"> - :o1 {</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ...</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[1] -voc:hasFile rdf:type rdf:Property ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdf:domain voc:Folder ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdf:range voc:File ; </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[2] - -nrl:inverseProperty voc:inFolder .</span><br style="font-family: monospace;" /> - - - - - <br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[3] -voc:inFolder rdf:type rdf:Property ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdf:domain voc:File ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdf:range voc:Folder ; </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[4] - - nrl:inverseProperty voc:hasFile . }</span></td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<h2><a class="mozTocH2" name="mozTocId929002"></a><a name="3._NRL_Named_Graph_Extensions"></a>3. -Handling -Multiple Models: NRL Named Graph Extensions</h2> - - - - -<p style="background-color: rgb(255, 255, 255); text-align: justify;">In -the Social Semantic Desktop -domain we -take a Named Graphs approach to semantic data. Named Graphs [NGs] are -an extension on top of RDF, where every RDF Graph as defined -in [<a href="#References">RDF -Specification - CONCEPTS</a>] is identified by -a name. -<span class=""></span>NGs -provide useful additional functionality on top of RDF, -particulary with respect to metametadata (data about metadata), -provenance and data (in)equivalence issues. <span style="background-color: rgb(255, 255, 51);"><span style="background-color: rgb(255, 255, 255);">This approach -is based on -the work</span> <span style="background-color: rgb(255, 255, 255);">described -in [</span></span><a style="background-color: rgb(255, 255, 255);" href="#References">NAMED -GRAPHS</a><span style="background-color: rgb(255, 255, 255);">] -excluding the open-world assumption described there. However, -one -should -note that our definitions for a closed-world and open-world assumption -(See Section <a href="#1.7_NRL_and_Closed_World_Vs._Open_World">1.7</a>) -differ slightly from the ones given in [</span><a style="background-color: rgb(255, 255, 255);" href="#References">NAMED -GRAPHS</a><span style="background-color: rgb(255, 255, 255);">].</span><span style="background-color: rgb(255, 255, 51);"><span style="background-color: rgb(255, 255, 255);"> -As -previously stated NRL does not assume an open-world scenario and -although it imposes no semantics per se to the graphs the NRL -Semantics are based on a closed-world assumption.</span></span></p> - - - - -<div style="text-align: justify; background-color: rgb(255, 255, 255);"> -<p>A -named graph is a pair <span style="font-style: italic;">(n,g)</span>, -where <span style="font-style: italic;">n</span> is -a unique URI -reference denoting the assigned name for the graph <span style="font-style: italic;">g</span>. Such a mapping<span style="font-style: italic;"> -</span>fixes -the graph <span style="font-style: italic;"> -</span><span style="font-style: italic;">g</span> -corresponding -to <span style="font-style: italic;">n -</span>in -a rigid, -non-extensible way<span style="font-style: italic;">.</span> -The URI representing <span style="font-style: italic;">n</span> -can then be used from any location to refer to the -corresponding set of triples belonging to the graph <span style="font-style: italic;">g</span>. In other words, -graph names, like namespaces, should be globally unique. A graph <span style="font-style: italic;">g'</span> -consistent with a -different graph <span style="font-style: italic;">g -</span>named -<span style="font-style: italic;">n -</span>cannot -be assigned the same name <span style="font-style: italic;">n</span>. -Two -different datasets asserting graphs -<span style="font-style: italic;">g</span> and <span style="font-style: italic;">g'</span> having -the same URI for a name contradict one another. </p> - - - - -</div> - - - - -<p style="text-align: justify;">An RDF -triple can exist in a -named graph or outside any named graph. However, for consistency -reasons, all triples must be assigned to some named graph. For -this reason, NRL provides -the special named graph [<a href="#3.1.7._nrl:DefaultGraph">nrl:DefaultGraph</a>]. -Triples existing outside any named graph automatically -form part of this default graph. -This ensures backward compatibility with triples that are not -based -on named graphs. This approach gives rise to the term RDF Dataset as -defined in [<a href="#References">SPARQL-QUERY</a>]. -An RDF dataset is composed of a default graph and an unlimited number -of distinct named graphs. It is formally defined as the set <span style="font-style: italic;">{g, (n</span><sub style="font-style: italic;">1</sub><span style="font-style: italic;">, -g</span><sub style="font-style: italic;">1</sub><span style="font-style: italic;">), (n</span><sub style="font-style: italic;">2</sub><span style="font-style: italic;">, -g</span><sub style="font-style: italic;">2</sub><span style="font-style: italic;">), . . ., (n</span><sub style="font-style: italic;">n</sub><span style="font-style: italic;">, -g</span><sub style="font-style: italic;">n</sub><span style="font-style: italic;">) }</span> comprising of -the default graph <span style="font-style: italic;">g</span> -and zero or more named graphs <span style="font-style: italic;">(n,g)</span>.</p> - - - - -<p style="background-color: rgb(255, 255, 255); text-align: justify;"><span style="background-color: rgb(255, 255, 255);">NRL -distinguishes between </span><span style="font-style: italic; background-color: rgb(255, 255, 255);">Graphs</span><span style="background-color: rgb(255, 255, 255);"> -and </span><span style="font-style: italic; background-color: rgb(255, 255, 255);">Graph -Roles</span><span style="background-color: rgb(255, 255, 255);">, -in -order to have orthogonal modeling -primitives for defining graphs and for specifying their role. A -graph role refers to the characteristics and content of a named graph -(e.g. simple data, an ontology, a knowledge base, etc.) and how the -data is intented to be handled. </span><span style="background-color: rgb(255, 255, 255);" class=""> -The NEPOMUK Annotation Ontology (Refer to the <a href="http://www.semanticdesktop.org/ontologies/nao">NAO</a>) -includes</span><span style="background-color: rgb(255, 255, 255);" class=""> -vocabulary for</span><span style="background-color: rgb(255, 255, 255);" class=""> providing -metadata about graph roles. </span><span style="background-color: rgb(255, 255, 255);">Graph -metadata -will be -attached to these roles rather than to the graphs themselves, because -in practice it makes more sense to describe an ontology or a -knowledge base rather than an anonymous graph. Roles are more stable -than the graphs they represent, and while the graph for a particular -role might change constantly, evolution of the role itself is less -frequent. An instantiation of a -role represents a specific type of graph and the -corresponding triple set data</span><span style="font-style: italic; background-color: rgb(255, 255, 255);"></span><span style="background-color: rgb(255, 255, 255);">. One -can contain graph metadata outside or inside the graph being described. -Storing graph metadata within the graph itself implies that the graph -metadata is also describing itself, which is not something one will -always want to have. Therefore its more suitable to keep graph metadata -separate from its respective graph, and therefore outside the graph. -This means to either contain the metadata in the default -graph, or -in a dedicated named graph. Since having graph metadata about every -existing named graph in the default graph is not practical, it is more -suitable to have the graph metadata in separate named graphs. That is, -any metadata about a named graph <span style="font-style: italic;">g</span> -will be contained within a separate -metadata graph <span style="font-style: italic;">gm</span> -dedicated for <span style="font-style: italic;">g</span>. -A special graph role, [<a href="#3.2.7._nrl:GraphMetadata">nrl:GraphMetadata</a>] -is used to mark such metadata graphs.</span></p> - - - - -<p style="background-color: rgb(255, 255, 255); text-align: justify;"><span style="background-color: rgb(255, 255, 255);"> -General graph -vocabulary is defined in [</span><a style="background-color: rgb(255, 255, 255);" href="#3.1._Graph_Core_Vocabulary_">Section -3.1</a><span style="background-color: rgb(255, 255, 255);">] -while [</span><a style="background-color: rgb(255, 255, 255);" href="#3.2._Graph_Roles_Vocabulary">Section -3.2</a><span style="background-color: rgb(255, 255, 255);">] -is dedicated entirely to graph roles. </span><a style="background-color: rgb(255, 255, 255);" href="#Fig3">Figure -3</a><span style="background-color: rgb(255, 255, 255);"> -depicts the class hierearchy supporting NGs -in NRL. Graph -Roles</span><span style="font-style: italic; background-color: rgb(255, 255, 255);"> -</span><span style="background-color: rgb(255, 255, 255);">(yellow) -are defined as a subclass of the abstract role superclass nrl:Data, -itself being defined as a subclass of the general -Graph -representation -(red). A special Graph specialization (blue) is used as a -marker -class for Graphs that are represented and identified by a -document URL [See </span><a style="background-color: rgb(255, 255, 255);" href="#3.1.2._nrl:DocumentGraph">3.1.2</a>]. -</p> - - - - -<div style="text-align: center;"><img src="NamedGraphs.png" alt="" style="width: 602px; height: 349px;" /><br /> - - - - -</div> - - - - -<p style="margin-left: 40px; text-align: center;"><a name="Fig3"></a>Figure -3: NRL Named Graph class -hierarchy</p> - - - - -<h3><a class="mozTocH3" name="mozTocId549245"></a><a name="3.1._Graph_Core_Vocabulary"></a>3.1. -Graph Core Vocabulary</h3> - - - - -<p>This section specifies -the core named graph vocabulary. This -consists of top-level named graph elements which represent general -graphs. Vocabulary for representation of specific graph roles is -described in section [<a href="#3.2._Graph_Roles_Vocabulary">3.2.</a>].</p> - - - - -<h4><a class="mozTocH4" name="mozTocId991762"></a><a name="3.1.1._nrl:Graph"></a>3.1.1. -nrl:Graph</h4> - - - - -<p>This class represents -a named graph. An instance of -this class will represent a named graph as described in the -introduction of this section, where the name of the instance coincides -with the name of the graph. It should be noted that all graph role -classes described in [<a href="#3.2._Graph_Roles_Vocabulary">3.2</a>] -are subclasses of this element [See <a href="#Fig3">Figure -3</a>]. -As such, there will generally be instances of specific graph -roles -rather than this more generic graph representation. This class is -similar to [<a href="http://www.w3.org/2004/03/trix/">rdfg:Graph</a>].</p> - - - - -<h4><a class="mozTocH4" name="mozTocId246095"></a><a name="3.1.2._nrl:DocumentGraph"></a>3.1.2. -nrl:DocumentGraph</h4> - - - - -<p style="text-align: justify;">This is a marker class -that names graphs via the URL of their containing document. A graph that is completely represented by -such a -document can be defined to be an instance of this class, whereby the -document URL will become the name of that graph. </p> - - - - -<h4><a class="mozTocH4" name="mozTocId178125"></a><a name="3.1.3._nrl:subGraphOf"></a>3.1.3. -nrl:subGraphOf</h4> - - - - -<p style="text-align: justify;">Graphs -can consist of subparts of other more -general -Graphs. In -other terms, a set of triples may form a specific part of a -more -general set of triples. This property can be used to model such a -relationship between two instances of [<a href="#3.1.1">nrl:Graph</a>]. -This -property is the inverse of [<a href="#3.1.4._nrl:superGraphOf">nrl:superGraphOf</a>]. -When a graph <span style="font-style: italic;">g</span> -is defined to be a subgraph of another graph <span style="font-style: italic;">g'</span>, the latter is -understood to be the supergraph of <span style="font-style: italic;">g</span>. -This -property is similar to [<a href="http://www.w3.org/2004/03/trix/">rdfg:subGraphOf</a>]. </p> - - - - -<h4><a class="mozTocH4" name="mozTocId972506"></a><a name="3.1.4._nrl:superGraphOf"></a>3.1.4. -nrl:superGraphOf</h4> - - - - -<p>This property can be -used to state that one graph subsumes -another -graph. A supergraph will then consist of one or more subgraphs. This -property is the inverse of [<a href="#3.1.3._nrl:subGraphOf">nrl:subGraphOf</a>]. -When a graph <span style="font-style: italic;">g' -</span>is -defined to be a supergraph of another graph <span style="font-style: italic;">g</span>, the latter is -understood to be a supgraph of <span style="font-style: italic;">g'</span>. -The property [<a href="#3.1.6._nrl:imports">nrl:imports</a>] -is a subproperty of this property.</p> - - - - -<h4><a class="mozTocH4" name="mozTocId503632"></a><a name="3.1.5._nrl:equivalentGraph"></a>3.1.5. -nrl:equivalentGraph</h4> - - - - -<div style="text-align: justify;">A set -of triples can -undergo duplication at a number of separate locations. This property -can effectively be used to state that a graph that manifests -itself at more than one location under -different names -is in fact equivalent. Equivalent graphs are simultaneously -the subgraph and supergraph of each other. This property is similar -to [<a href="http://www.w3.org/2004/03/trix/">rdfg:equivalentGraph</a>].<br /> - - - - -</div> - - - - -<span class=""><span style="font-style: italic; background-color: rgb(255, 255, 255);"><br /> - - - - -<span style="font-weight: bold;">Note</span></span><span style="background-color: rgb(255, 255, 255);"><span style="font-weight: bold;">:</span> The -term equivalentGraph -is subject to the role of the graphs being related. Hence for two -graphs to be defined equivalent, they must either -have the same role, or be a superrole or subrole of each other -as depicted -in </span><a style="background-color: rgb(255, 255, 255);" href="#Fig3">Figure -3</a><span style="background-color: rgb(255, 255, 255);">. -When a -graph </span><span style="font-style: italic; background-color: rgb(255, 255, 255);">g</span><span style="background-color: rgb(255, 255, 255);"> -having a role </span><span style="font-style: italic; background-color: rgb(255, 255, 255);">R -</span><span style="background-color: rgb(255, 255, 255);">is -defined to be equivalent to a graph </span><span style="font-style: italic; background-color: rgb(255, 255, 255);">g'</span><span style="background-color: rgb(255, 255, 255);"> having a -superrole </span><span style="font-style: italic; background-color: rgb(255, 255, 255);">R'</span><span style="background-color: rgb(255, 255, 255);">, -then </span><span style="font-style: italic; background-color: rgb(255, 255, 255);">g' -</span><span style="background-color: rgb(255, 255, 255);">is -understood to have the more specific role </span><span style="font-style: italic; background-color: rgb(255, 255, 255);">R</span><span style="background-color: rgb(255, 255, 255);">. For example, -if -graph </span><span style="font-style: italic; background-color: rgb(255, 255, 255);">g -</span><span style="background-color: rgb(255, 255, 255);">having -role [<a href="#3.2.4._nrl:Ontology">nrl:Ontology</a>] -is defined as equivalent to graph </span><span style="font-style: italic; background-color: rgb(255, 255, 255);">g'</span><span style="background-color: rgb(255, 255, 255);"> having role -[<a href="#3.2.2._nrl:Schema">nrl:Schema</a>], -then -it can be said that graph </span><span style="font-style: italic; background-color: rgb(255, 255, 255);">g'<span style="font-style: italic;"><span style="font-style: italic;"> </span></span></span><span style="background-color: rgb(255, 255, 255);">has -a role of [<a href="#3.2.4._nrl:Ontology">nrl:Ontology</a>]. -However not all graphs can be defined to be -equivalent. For example, graph </span><span style="font-style: italic; background-color: rgb(255, 255, 255);">g</span><sub style="font-style: italic; background-color: rgb(255, 255, 255);">1</sub><span style="font-style: italic; background-color: rgb(255, 255, 255);"> -</span><span style="background-color: rgb(255, 255, 255);">having -role -[<a href="#3.2.3._nrl:InstanceBase">nrl:InstanecBase</a>] -cannot be defined as equivalent to graph </span><span style="font-style: italic; background-color: rgb(255, 255, 255);">g</span><sub style="font-style: italic; background-color: rgb(255, 255, 255);">2</sub><span style="background-color: rgb(255, 255, 255);"> if -this graph has the role </span></span><span class=""><span style="background-color: rgb(255, 255, 255);">[<a href="../../l#3.2.2._nrl:Schema">nrl:Schema</a>]</span></span><span class=""><span style="background-color: rgb(255, 255, 255);">.</span><br /> - - - - -</span><span style="font-weight: bold;"></span> -<h4><a class="mozTocH4" name="mozTocId858885"></a><a name="3.1.6._nrl:imports"></a>3.1.6. -nrl:imports</h4> - - - - -<div style="text-align: justify;"> -<p>This special subproperty -of [<a href="#3.1.4._nrl:superGraphOf">nrl:superGraphOf</a>] -models graph imports and can be used to state that an existing named -graph <span style="font-style: italic;">g'</span> -should be considered as part of graph <span style="font-style: italic;">g</span>. -This is akin to -saying that <span style="font-style: italic;">g'</span> -is a subgraph of <span style="font-style: italic;">g</span> -or inversely that <span style="font-style: italic;">g</span> -is a supergraph of <span style="font-style: italic;">g'</span>. -This property can be used to model graph role data imports. Importing a -graph into another means that all the former graph’s data, -and semantics, -will implicitly form part of the latter.<span style="font-style: italic;"></span><span style="font-style: italic;"></span> -Such modelling is transitive. If graph<span style="font-style: italic;"> -g</span> is imported into -graph <span style="font-style: italic;">g'</span>, -and <span style="font-style: italic;">g'</span> is -imported into graph <span style="font-style: italic;">g''</span>, -then <span style="font-style: italic;">g''</span> -also includes the data represented by<span style="font-style: italic;"><span style="font-style: italic;"> </span>g</span>. -Two graphs <span style="font-style: italic;">g</span> -and <span style="font-style: italic;">g'</span> -are equivalent if they import each other. When applied to the [<a href="#3.2.4._nrl:Ontology">nrl:Ontology</a>] -role this property -can be used to model ontology imports and in this case this -property is -similar to [<a href="http://www.w3.org/TR/owl-ref/#imports-def">owl:imports</a>]. -<span style="background-color: rgb(255, 255, 255);">An -incompatibility problem may arise when importing graphs with -incompatible semantics to the current graph, or combining multiple -graphs with different semantics into a new supergraph.. This -incompatibility may however be resolved via semantic views which -rectify this problem by aligning the different semantics of the graphs.</span></p> - - - - -</div> - - - - -<h4><a class="mozTocH4" name="mozTocId337127"></a><a name="3.1.7._nrl:DefaultGraph"></a>3.1.7. -nrl:DefaultGraph</h4> - - - - -<div style="text-align: justify;"> -<p>Although triples can exist inside a named graph or -outside any -named graph, for consistency reasons all triples are required to form -part of some named <span style="background-color: rgb(255, 255, 255);">graph. -This -default graph instance is provided by -NRL to serve this requirement. All triples existing outside any named -graph</span><span style="background-color: rgb(255, 255, 255);"> -(e.g. external triples unaware of NRL's named graph approach), -will be assigned to this default graph. The -DefaultGraph is disjoint from all other existing named graphs and it is -given by the intersection of the complements of all other existing -named graphs in the RDF triple space.</span></p> - - - - -</div> - - - - -<h3><a class="mozTocH3" name="mozTocId787923"></a><a name="3.2._Graph_Roles_Vocabulary"></a><span style="font-weight: bold;"></span>3.2. -Graph -Roles Vocabulary </h3> - - - - -<div style="text-align: justify;"> -<p>This section introduces -classes and properties provided in NRL that -deal with Graph Roles as described in the introduction of <a href="#3._NRL_Named_Graph_Extensions">Section 3</a> -and -depicted in <a href="#Fig3">Figure -3</a>. This vocabulary is closely tied with the Graph Metadata -Vocabulary provided in [<a href="http://www.semanticdesktop.org/ontologies/nao">NAO</a>]. -In fact they can also be considered as graph metadata vocabulary, since -the elements are in practice used within graph metadata definitions. -However, due to their essential nature they are core NRL elements. </p> - - - - -</div> - - - - -<h4><a class="mozTocH4" name="mozTocId792849"></a><a name="3.2.1._nrl:Data"></a>3.2.1. -nrl:Data</h4> - - - - -<div style="text-align: justify;"> -<p>This is an abstract -class -representing all graph roles. All graphs are assigned one of -the -roles represented by this abstract superclass. It is itself a subclass -of [<a href="#3.1.1._nrl:Graph">nrl:Graph</a>] -alongside [<a href="#4.1.1_nrl:GraphView">nrl:GraphView</a>] -and [<a href="#3.1.2._nrl:DocumentGraph">nrl:DocumentGraph</a>].</p> - - - - -<h4><a class="mozTocH4" name="mozTocId420122"></a><a name="3.2.2._nrl:Schema"></a>3.2.2. -nrl:Schema</h4> - - - - -</div> - - - - -<div style="text-align: justify;"> -<p>A -schema represents a -conceptualisation model. This class is used as a role for a graph that -represents data in the -form of a schema. It is defined as a subclass of [<a href="#3.2.1._nrl:Data">nrl:Data</a>], -and -therefore also a subclass of [<a href="#3.1.1._nrl:Graph">nrl:Graph</a>]; -and it -is a superclass of [<a href="#3.2.4._nrl:Ontology">nrl:Ontology</a>].</p> - - - - -<h4><a class="mozTocH4" name="mozTocId196061"></a><a name="3.2.3._nrl:InstanceBase"></a>3.2.3. -nrl:InstanceBase</h4> - - - - -<p>A graph may represent instances of classes -defined -using some schema (or ontology) that is represented by another separate -graph. This class provides the representation for such graphs. An -instance base is a -subclass of [<a href="#3.2.1._nrl:Data">nrl:Data</a>], -and therefore also a subclass of -[<a href="#3.1.1._nrl:Graph">nrl:Graph</a>].</p> - - - - -<h4><a class="mozTocH4" name="mozTocId287595"></a><a name="3.2.4._nrl:Ontology"></a>3.2.4. -nrl:Ontology</h4> - - - - -<p>An ontology is a more expressive type of schema describing -more complex -models which may include rule-based knowledge in addition to a -relational characterisation. This class represents such a role for a -Graph and it can also serve the -purpose of an ontology header within RDF/S documents as provided by [<a href="http://www.w3.org/TR/owl-ref/#Ontology-def">owl:Ontology</a>]. -This class is a subclass of [<a href="#3.2.2._nrl:Schema">nrl:Schema</a>] -and therefore also a subclass -of -[<a href="#3.2.1._nrl:Data">nrl:Data</a>] -and [<a href="#3.1.1._nrl:Graph">nrl:Graph</a>].</p> - - - - -<h4><a class="mozTocH4" name="mozTocId372280"></a><a name="3.2.5._nrl:KnowledgeBase"></a>3.2.5. -nrl:KnowledgeBase</h4> - - - - -<p>A graph can represent a schema (or ontology) together -with a -number of instantiations of elements in the same schema (or ontology). -Such a graph has a similar role to an instance base with the major -difference that it also represents the schema (or ontology) providing -the constructs used to define the instances. Therefore this -role can be seen as a subset of the -intersection of the [<a href="#3.2.4._nrl:Ontology">nrl:Ontology</a>] -and [<a href="#3.2.3._nrl:InstanceBase">nrl:InstanceBase</a>] -roles, and is in -fact defined as a subclass of both these roles. -</p> - - - - -</div> - - - - -<h4><a class="mozTocH4" name="mozTocId379616"></a><a name="3.2.6._nrl:Configuration"></a>3.2.6. -nrl:Configuration</h4> - - - - -<div style="text-align: justify;"> -<p>Technical -configuration -data that is -irrelevant to general semantic web data can also be -represented -within a graph, through this role. Other additional roles serving -different purposes might be added in the future. This class is a -subclass of [<a href="#3.2.1._nrl:Data">nrl:Data</a>]. -</p> - - - - -<h4><a class="mozTocH4" name="mozTocId781665"></a><a name="3.2.7._nrl:GraphMetadata"></a>3.2.7. -nrl:GraphMetadata</h4> - - - - -<p>This role is useful to mark graphs whose sole purpose is to -store -metadata about some specific graph. Data about a graph, or Graph -Metadata, is thus stored in a corresponding graph that has -this -role. -</p> - - - - -</div> - - - - -<h4><a class="mozTocH4" name="mozTocId159397"></a><a name="3.2.8._nrl:graphMetadataFor"></a><span style="background-color: rgb(255, 255, 255);">3.2.8. -nrl:graphMetadataFor</span></h4> - - - - -<div style="background-color: rgb(255, 255, 255);"> -<p>This -property binds a metadata graph to the graph being -described. A metadata graph must point to the named graph being -described therefore the minimum cardinality is set to 1. Given that in -some cases a single metadata graph can provide metadata for multiple -graphs, the maximum cardinality is undefined. </p> - - - - -</div> - - - - -<h4 style="background-color: rgb(255, 255, 255);"><a class="mozTocH4" name="mozTocId728175"></a><a style="background-color: rgb(255, 255, 255);" name="3.2.9._nrl:coreGraphMetadataFor"></a><span style="background-color: rgb(255, 255, 255);">3.2.9. -nrl:coreGraphMetadataFor</span></h4> - - - - -<div style="text-align: justify; background-color: rgb(255, 255, 255);"> -<p style="background-color: rgb(255, 255, 255);">Although -a graph can have multiple metadata graphs that describe it, -there can only be one unique core metadata graph which defines the -graph's important core properties, e.g. whether it is updatable or -otherwise and other important metadata -vocabulary. This property identifies such a core metadata graph and -points to the graph it describes. It is a subproperty of <a href="#3.2.8._nrl:graphMetadataFor">nrl:graphMetadataFor</a>.<br /> - - - - -</p> - - - - -<span style="font-style: italic;"><span style="font-weight: bold; background-color: rgb(255, 255, 255);">Note:</span><span style="background-color: rgb(255, 255, 255);"> -Sometimes the inverse link (from the subject named graph to its core -metadata graph) might be of practical use. However, in order to avoid -redundancy in the language, this direction has not been included in -NRL. For a more efficient access to a graph's metadata, specific -applications might want to establish this direction when loading graphs.</span></span> -</div> - - - - -<h4 style="background-color: rgb(255, 255, 255);"><a class="mozTocH4" name="mozTocId465236"></a><a name="3.2.10._nrl:Semantics"></a>3.2.10. -nrl:Semantics</h4> - - - - -<div style="text-align: justify;"> -<p><span style="background-color: rgb(255, 255, 255);">The -declarative semantics for a graph role can be specified by -referring to instances of this class. Such an instance will consist of -an identifier to a location where the formal semantics of the schema or -language used are specified.</span></p> - - - - -<h4><a class="mozTocH4" name="mozTocId737534"></a><span style="background-color: rgb(255, 255, 255);"></span><a name="3.2.11._nrl:hasSemantics"></a>3.2.11. -nrl:hasSemantics</h4> - - - - -<p><span style="background-color: rgb(255, 255, 255);">Graph -roles -do not automatically have any semantics, but these can be -specified through this property (declarative -semantics) with respect -to an instance of the special class [<a href="#3.2.10._nrl:Semantics">nrl:Semantics</a>]. -The semantics of a -graph role can also be realized (procedural semantics) by -instantiating a graph view with a semantic -specification over the role (See </span><a style="background-color: rgb(255, 255, 255);" href="#4._Graph_Views_Extensions">Graph Views -Extensions</a><span style="background-color: rgb(255, 255, 255);"> and <a href="#4.2.2._nrl:realizes">nrl:realizes</a>). However -this property has a declarative rather than a procedural role.</span></p> - - - - -<span style="background-color: rgb(255, 255, 255);"></span><span style="background-color: rgb(255, 255, 255);"></span><span style="background-color: rgb(255, 255, 255);"><span style="font-style: italic; font-weight: bold;">Note:</span> -A graph role -with (virtual) declarative semantics -should never be assumed to also carry (realized) procedural -semantics. </span><br /> - - - - -</div> - - - - -<h4 style="background-color: rgb(255, 255, 255);"><a class="mozTocH4" name="mozTocId331701"></a><a name="3.2.12._nrl:semanticsDefinedBy"></a>3.2.12. -nrl:semanticsDefinedBy</h4> - - - - -<div style="text-align: justify;"> -<p><span style="background-color: rgb(255, 255, 51);"><span style="background-color: rgb(255, 255, 255);">This -property links instances of the </span></span><span style="background-color: rgb(255, 255, 255);">[<a href="../../l#3.2.10._nrl:Semantics">nrl:Semantics</a>]</span><span style="background-color: rgb(255, 255, 51);"><span style="background-color: rgb(255, 255, 255);"> class to a -URL for a document that defines the formal, non-machine-readable -semantics that the instance is representing.</span></span></p> - - - - -<span style="background-color: rgb(255, 255, 51);"></span></div> - - - - -<h4 style="background-color: rgb(255, 255, 255); text-align: justify;"><a class="mozTocH4" name="mozTocId704028"></a><a name="3.2.13._nrl:semanticsLabel"></a>3.2.13. -nrl:semanticsLabel</h4> - - - - -<div style="text-align: justify;"> -<p><span style="background-color: rgb(255, 255, 255);">This -trivial property assigns a string label to instances of the </span><span style="background-color: rgb(255, 255, 255);">[<a href="../../l#3.2.10._nrl:Semantics">nrl:Semantics</a>]</span><span style="background-color: rgb(255, 255, 255);"> -class, in order to more easily identify and refer to different -semantics.</span></p> - - - - -<p><span style="background-color: rgb(255, 255, 255);"></span></p> - - - - -<h4 style="background-color: rgb(255, 255, 255);"><a class="mozTocH4" name="mozTocId379929"></a><a name="3.2.14._nrl:updatable"></a>3.2.14. -nrl:updatable</h4> - - - - -<p style="background-color: rgb(255, 255, 255);"><span style="font-weight: normal;">A -graph role is stated as being -updatable (1) or static (0). A static graph prevents any modifications -- any modified versions of the graph must be created as a separate -graph. A non-static graph's dataset can be directly modified.</span></p> - - - - -<p><span style="background-color: rgb(255, 255, 255);"> -</span></p> - - - - -</div> - - - - -<h3><a class="mozTocH3" name="mozTocId54895"></a><a name="3._Named_Graph_Example"></a>3. -Named Graph Example</h3> - - - - -<div style="text-align: justify;"> -<p>The following example -demonstrates the use of NG extensions and is based on <a href="http://www.wiwiss.fu-berlin.de/suhl/bizer/TriG/">TriG</a> -[TRIG] as introduced in the introduction of this document. A simple -graph in TriG -named G (where g is a URI) is syntactically denoted by: -</p> - - - - -</div> - - - - -<table style="text-align: left; width: 100%; height: 32px;" border="1" cellpadding="2" cellspacing="2"> - - - - - <tbody> - - - - - <tr> - - - - - <td style="width: 100%;"> - - - - <div style="text-align: center; margin-left: 40px;">:G -{<span style="font-style: italic;">Triple Set</span>}<br /> - - - - - </div> - - - - - </td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<div style="margin-left: 40px;"><br /> - - - - -</div> - - - - -<p>This example and the one -that follows in [<a href="#4.3_Graph_Views_Example">Section -4.3</a>] model -the dataflow represented in <a href="#Fig2">Figure -2</a>. -This example demonstrates how one can make use of the named graph -paradigm and the syntax for named graphs presented in this -section. <br /> - - - - -</p> - - - - -<div style="text-align: justify; background-color: rgb(255, 255, 255);"><span style="font-style: italic;"></span>[1] The -example starts by defining the -required namespaces.<br /> - - - - -<br /> - - - - -[2-7] Metadata about six -different graphs is represented within four metadata graphs. <br /> - - - - -<br /> - - - - -[3] The metadata graph describing graph <span style="font-style: italic;">ex:o1</span> -given in [8] states that <span style="font-style: italic;">ex:o1</span> -is an ontology (graph with role ontology). <span style="font-style: italic;"><br /> - - - - -<br /> - - - - -</span>[4] <span style="font-style: italic;">ex:o1 </span>is -defined to have the declarative semantics defined by the instance <span style="font-style: italic;">RDFS</span>.<br /> - - - - -<br /> - - - - -[5] <span style="font-style: italic;">RDFS</span> -is an instance of -nrl:Semantics. It is labelled 'RDF/S' and its semantics are said to be -defined by 'http://www.w3.org/TR/rdf-schema#'.<br /> - - - - -<br /> - - - - -<span style="font-style: italic;"></span>[6] <span style="font-style: italic;">ex:o1_metadata </span>itself -is marked as being graph metadata.<br /> - - - - -<span style="font-style: italic;"></span><br /> - - - - -[7] <span style="font-style: italic;">ex:o2_metadata </span>says -that <span style="font-style: italic;">ex:o2</span> -is graph equivalent to <span style="font-style: italic;">http://www.domain.com/o2.rdfs. </span><br /> - - - - -<span style="font-style: italic;"></span><br /> - - - - -[8] <span style="font-style: italic;">ex:o2_metadata</span> states -also that <span style="font-style: italic;">ex:o </span>is -an ontology represented by the union of graphs <span style="font-style: italic;">ex:o1</span> and <span style="font-style: italic;">ex:o2</span>. <span style="font-style: italic;">ex:o</span> is now a -supergraph of <span style="font-style: italic;">ex:o1</span> -and <span style="font-style: italic;">ex:o2</span> -(or <span style="font-style: italic;">http://www.domain.com/o2.rdfs</span>). -Inversely the named graphs are subgraphs of <span style="font-style: italic;">ex:o</span>.<br /> - - - - -<br /> - - - - -[9] <span style="font-style: italic;">ex:ib1_metadata </span>states -that <span style="font-style: italic;">ex:ib1 </span>is -an instance base defined in [9].<br /> - - - - -<br /> - - - - -[10] <span style="font-style: italic;">ex:kb1_metadata</span> -states that <span style="font-style: italic;">ex:kb1 </span>is -a knowledge base graph represented by the union of graphs <span style="font-style: italic;">ex:o</span>,<span style="font-style: italic;"> ex:ib1 </span>and<span style="font-style: italic;"> </span><span style="font-style: italic;">http://www.anotherdomain.com/ib2.rdf</span>s. -Alternatively, through the definition of <span style="font-style: italic;">ex:o </span>[5], one can -say that <span style="font-style: italic;">ex:kb1</span> -is represented by the union of graphs <span style="font-style: italic;">ex:o1</span>, -<span style="font-style: italic;">ex:o2 </span>(or<span style="font-style: italic;"> </span><span style="font-style: italic;">http://www.domain.com/o2.rdfs</span>), -<span style="font-style: italic;">ex:ib1</span> and <span style="font-style: italic;">http://www.anotherdomain.com/ib2.rdfs</span>, -where the latter graphs are all subgraphs of <span style="font-style: italic;">ex:kb1</span>.<br /> - - - - -<br /> - - - - -<span style="font-style: italic;"> -</span>[12] The representation for graph <span style="font-style: italic;">ex:o1</span> (an ontology) -is composed of the definition of a class <span style="font-style: italic;">ex:Person</span>, a class -ex:<span style="font-style: italic;">DesktopUser</span> -which is also a subclass of <span style="font-style: italic;">ex:Person</span>, -and a symmetric property <span style="font-style: italic;">ex:knows</span> -which relates instances of <span style="font-style: italic;">ex:Person</span> -to other -instansces of <span style="font-style: italic;">ex:Person</span>.<br /> - - - - -<br /> - - - - -[12] The representation for graph <span style="font-style: italic;">ex:ib1 -</span>(an instance base) is composed of the definition of an -instance of <span style="font-style: italic;">ex:DesktopUser -</span>called <span style="font-style: italic;">ex:User1</span>, -and two instances of <span style="font-style: italic;">ex:Person</span> -called <span style="font-style: italic;">ex:Contact1</span> -and <span style="font-style: italic;">ex:Contact2</span>. -<span style="font-style: italic;">ex:Contact1</span> -'knows' <span style="font-style: italic;">ex:Contact2</span> -and <span style="font-style: italic;">ex:User1</span> -while ex:Contact2 'knows' <span style="font-style: italic;">ex:User1</span>. -However since <span style="font-style: italic;">ex:knows </span>is -a symmetric property, all three instances of <span style="font-style: italic;">ex:Person</span> (or its -subclass <span style="font-style: italic;">ex:DesktopUser</span>) -'know' each other.<br /> - - - - -<br /> - - - - -<table style="text-align: left; font-family: monospace; width: 100%;" border="1" cellpadding="2" cellspacing="2"> - - - - - <tbody> - - - - - <tr> - - - - - <td><span style="font-family: monospace;">[1] - @prefix nrl: -<http://www.semanticdesktop.org/ontology/yyyy/mm/dd/nrl#> -.</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - @prefix ex: -<http://www.example.org/vocabulary#> .</span><br style="font-family: monospace;" /> - - - - - <br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[2] - ex:o1_metadata { </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[3] - ex:o1 a nrl:Ontology ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[4] - nrl:hasSemantics ex:RDFS .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[5] - ex:RDFS a nrl:Semantics ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - -nrl:semanticsDefinedBy "http://www.w3.org/TR/rdf-schema#" ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - -nrl:semanticsLabel "RDF/S" . </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[6] - ex:o1_metadata rdf:type nrl:GraphMetadata . }</span><br style="font-family: monospace;" /> - - - - - <br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ex:o2_metadata { </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[7] - ex:o2 rdf:type nrl:Ontology ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - -nrl:equivalentGraph <http://www.domain.com/o2.rdfs> . </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[8] - ex:o rdf:type nrl:Ontology ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - nrl:imports ex:o1 ,</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - ex:o2 . </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ex:o2_metadata rdf:type nrl:GraphMetadata . }</span><br style="font-family: monospace;" /> - - - - - <br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[9] - ex:ib1_metdata {</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ex:ib1 rdf:type nrl:InstanceBase .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ex:ib1_metadata rdf:type nrl:GraphMetadata . }</span><br style="font-family: monospace;" /> - - - - - <br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[10] -ex:kb1_metadata {</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ex:kb1 rdf:type nrl:KnowledgeBase ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - nrl:imports ex:o , </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - ex:ib1 , </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - -<http://www.anotherdomain.com/ib2.rdfs> . </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ex:kb1_metadata rdf:type nrl:GraphMetadata . }</span><br style="font-family: monospace;" /> - - - - - <br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[11] ex:o1 { </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ex:Person rdf:type rdfs:Class .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ex:DesktopUser rdf:type rdfs:Class ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - rdfs:subClassOf ex:Person .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ex:knows rdf:type rdf:Property ,</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - nrl:SymmetricProperty ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - rdfs:domain -ex:Person ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - rdfs:range -ex:Person . }</span><br style="font-family: monospace;" /> - - - - - <br /> - - - - - <span style="font-family: monospace;">[12] ex:ib1 { </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> -ex:User1 rdf:type ex:DesktopUser .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ex:Contact1 rdf:type ex:Person ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - ex:knows ex:User1 ,</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - -ex:Contact1 .</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> -ex:Contact2 rdf:type ex:Person ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - ex:knows ex:User1 . } </span></td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<br /> - - - - -<p>The -RDF/S Ontology -accesible at <span style="font-style: italic;">http://www.domain.com/o2.rdfs</span> -and serialized as RDF/XML is given and described as follows.</p> - - - - -[1] Required namespaces are defined.<br /> - - - - -<br /> - - - - -[2] The [<a href="#3.2.4._nrl:Ontology">nrl:Ontology</a>] -class -can be used to define some (ontology) graph metadata about the graph -represented by this RDF/S document. Here it states that this is -a document graph having the role of an ontology. <br /> - - - - -<span style="font-style: italic; background-color: rgb(255, 255, 255);"><br /> - - - - -<span style="font-weight: bold;">Note:</span> -Although this is allowed it is not considered best practice, since in -this way, given that we state that XML/RDFS files can only encode one -graph at a time, one is effectively providing graph metadata within the -graph itself. This goes against our notion of keeping metadata about a -graph separate from the graph itself, as discussed in [<a href="#3._NRL_Named_Graph_Extensions">Section 3</a>].</span><br style="background-color: rgb(255, 255, 51);" /> - - - - -<br /> - - - - -[3] A class <span style="font-style: italic;">Desktop</span> -is defined.<br /> - - - - -<br /> - - - - -[4] A property <span style="font-style: italic;">user</span> -is defined as relating instances of <span style="font-style: italic;">Desktop -</span>to -instances of <span style="font-style: italic;">http://www.example.org/vocabulary#DesktopUser -</span>defined in <span style="font-style: italic;">ex:g1 -</span>in the example above.<br /> - - - - -<br /> - - - - -<table style="text-align: left; width: 100%;" border="1" cellpadding="2" cellspacing="2"> - - - - - <tbody> - - - - - <tr> - - - - - <td><span style="font-family: monospace;">[1] -<rdf:RDF</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> -xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> -xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> -xmlns:nrl="http://www.semanticdesktop.org/ontology/yyyy/mm/dd/nrl#"></span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> -xmlns="http://www.domain.com/o2#"></span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[2] -<nrl:Ontology rdf:about=""></span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> -<rdf:type rdfs:resource="nrl#DocumentGraph"/></span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> -<!--Other Graph Metadata---></span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> -</nrl:Ontology></span><br style="font-family: monospace;" /> - - - - - <br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[3] -<rdfs:Class rdf:ID="Desktop"/> </span><br style="font-family: monospace;" /> - - - - - <br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[4] -<rdf:Property rdf:ID="user"></span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> -<rdfs:domain rdf:resource="#Desktop"/></span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> -<rdfs:range -rdf:resource="http://www.example.org/vocabulary#DesktopUser/> </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> -</rdf:Property></span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - </rdf:RDF></span></td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<br /> - - - - -</div> - - - - -The following is the -RDF/S instance base -serialized as RDF/XML and accessible at <span style="font-style: italic;">http://www.anotherdomain.com/ib2.rdf</span>s:<br /> - - - - -<div style="margin-left: 40px;"> -<div style="text-align: justify;"><br /> - - - - -</div> - - - - -</div> - - - - -<div style="text-align: justify;">[1] Required namespaces -are defined.<br /> - - - - -<br /> - - - - -[2] Metadata about the instance base graph represented by this RDF/S -document is defined through the use of [<a href="#3.2.3._nrl:InstanceBase">nrl:InstanceBase</a>].<br /> - - - - -<span style="font-style: italic;"><span style="background-color: rgb(255, 255, 51);"></span></span><br /> - - - - -<span style="font-style: italic; background-color: rgb(255, 255, 255);"><span style="font-weight: bold;">Note:</span> Although this -is allowed it is -not considered best practice, since in this way, given that we state -that XML/RDFS files can only encode one graph at a time, one is -effectively providing graph metadata within the graph itself. This goes -against our notion of keeping metadata about a graph separate from the -graph itself, as discussed in [<a href="#3._NRL_Named_Graph_Extensions">Section 3</a>].</span><br style="background-color: rgb(255, 255, 51);" /> - - - - -<span style="font-style: italic;"></span><br /> - - - - -<span style="font-style: italic;"></span>[3] <span style="font-style: italic;">DesktopA </span>is -defined as an instance of <span style="font-style: italic;">o2:Desktop -</span>and related to <span style="font-style: italic;">http://www.example.org/vocabulary#User1 -</span>through the <span style="font-style: italic;">o2:user</span> -property. -<br /> - - - - -<br style="font-family: monospace;" /> - - - - -<table style="text-align: left; width: 100%;" border="1" cellpadding="2" cellspacing="2"> - - - - - <tbody> - - - - - <tr> - - - - - <td><span style="font-family: monospace;">[1] -<rdf:RDF</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> -xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> -xmlns:nrl="http://www.semanticdesktop.org/ontology/yyyy/mm/dd/nrl#"</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> -xmlns:o2="http://www.domain.com/o2#"</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> -xmlns="http://www.anotherdomain.com/ib2#"></span><br style="font-family: monospace;" /> - - - - - <br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[2] -<nrl:InstanceBase rdf:about=""></span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> -<rdf:type rdfs:resource="nrl#DocumentGraph"/></span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> -<!--Other Graph Metadata---></span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - </nrl:InstanceBase></span><br style="font-family: monospace;" /> - - - - - <br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[3] -<o2:Desktop rdf:ID="DesktopA"></span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> -<o2:user http://www.example.org/vocabulary#User1></span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - </o2:Desktop></span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - </rdf:RDF></span></td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<br /> - - - - -</div> - - - - -<h2><a class="mozTocH2" name="mozTocId172834"></a><a name="4._Graph_Views_Extensions"></a>4. Imposing -Semantics on and Tailoring of Graphs: NRL Graph Views<span style="background-color: rgb(255, 255, 255);"> Extensions</span></h2> - - - - -<div style="text-align: justify;"> -<p>A simple named -graph consists only of the enumerated triples in the -triple set associated with the name, and it does not inherently carry -any form of semantics. However in many situations it is desirable to -work -with an extended or restricted interpretation of a -simple syntax-only named graph. -These interpretations can be realized by applying rules which -enhance named graphs with entailment triples, or return a -restricted form of the -complete triple set. To preserve the integrity of a named graph, -interpretations of a basic named graph should -never replace the original. To model this functionality in an intuitive -way, while still separating between an original named graph and any -number of its interpretations, we introduce the concept of <span style="font-style: italic;">Graph Views</span>.</p> - - - - -<p>Graph views, -or simply views, are different interpretations for a -particular named graph. Formally, a graph view is an executable -specification of an input graph into a corresponding output graph. -Informally, they can be seen as arbitrary wrappings for a -named graph. <a href="#Fig4">Figure 4</a> -depicts -graph view support in -NRL. As can be seen in the figure, views are themselves named graphs -(subclass of <a href="#3.1.1._nrl:Graph">nrl:Graph</a>). -Therefore it is possible to have a named graph that is itself a -different interpretation, or view, of another named graph. This -modelling can be applied recurrently, yielding a view of a view (or an -interpretation of a named graph interpretation, as depicted in <a href="#Fig2">Figure 2</a>) and so on.<br /> - - - - -</p> - - - - -</div> - - - - -<div style="text-align: justify;"> -<div style="text-align: center;"> -<div style="text-align: center;"><span style="font-style: italic;"><img style="width: 555px; height: 325px;" alt="Graph Views Overview" src="GraphViews.png" /><br /> - - - - -</span><a name="Fig4"></a> -Figure 4: -Graph Views in NRL<br /> - - - - -</div> - - - - -</div> - - - - -<p>Views are -defined through <span style="font-style: italic;">View -Specifications</span> which -can execute, via a set of rules in a rule language (e.g. a -SPARQL -query over a named graph), or via an external application (e.g. an -application that performs and returns the transitive closure of -rdfs:subClassOf), the<span style="font-style: italic;"> -View Realization</span> for a particular view. As in the latter -example, view realizations can also realize the implicit -semantics of a graph according to some language -or schema (e.g. RDFS, OWL, NRL etc.). We refer to such -a view as a <span style="font-style: italic;">Semantic -View </span>and in <a href="#Fig4">Figure -4</a> -these are represented by the intersection of [<a href="#4.1.1_nrl:GraphView">nrl:GraphView</a>] -and <span style="font-style: italic;">Graph Roles</span>. -Therefore a semantic view is an instance of graph view that also -carries a particular graph role. Semantic views are also depicted in <a href="#Fig1">Figure -1</a>, and one can quite easily draw a parallel between the two -figures. One must note that the property [<a href="#4.2.2._nrl:realizes">nrl:realizes</a>] -applies -only to semantic views, since only such views realize an explicit form -of semantics. One should also note that in -contrast to graph roles which have only <span style="font-style: italic;">Declarative -Semantics</span> defined through the [<a href="#3.2.11._nrl:hasSemantics">nrl:hasSemantics</a>] -property, -semantic views also carry <span style="font-style: italic;">Procedural -Semantics</span>, -since the semantics of these graphs are always realized and not -simply assumed. </p> - - - - -</div> - - - - -<h3><a class="mozTocH3" name="mozTocId238972"></a><a name="4.1._Views_Core_Vocabulary"></a>4.1. Views -Core Vocabulary</h3> - - - - -<div style="text-align: justify;"> -<p>This section presents -the core vocabulary supporting views in NRL, -consisting of the core attributes that apply to views. The -following section is specifically dedicated to vocabulary concerning -the -specification of views.</p> - - - - -</div> - - - - -<h4 style="text-align: justify;"><a class="mozTocH4" name="mozTocId304281"></a><a name="4.1.1_nrl:GraphView"></a>4.1.1. -nrl:GraphView </h4> - - - - -<div style="text-align: justify;"> -<p>This class represents a -view over a named graph as introduced in this -document, and is itself modeled as a -subclass of a named graph. A view is realized through a view -specification, defined by an instance of [<a href="#4.2.1._nrl:ViewSpecification">nrl:ViewSpecification</a>]. -The view is linked its view specification through the [<a href="#4.1.3_nrl:hasSpecification">nrl:hasSpecification</a>] -property whereas the named graph that the view applies to is linked by [<a href="#4.1.2_nrl:viewOn">nrl:viewOn</a>]. -An instance of this class will be a realized view over -some named graph, and it will consist of the extended or restricted set -of RDF -triples present in the original named graph. -</p> - - - - -</div> - - - - -<h4 style="text-align: justify;"><a class="mozTocH4" name="mozTocId595657"></a><a name="4.1.2_nrl:viewOn"></a>4.1.2. -nrl:viewOn</h4> - - - - -<div style="text-align: justify;"> -<p>This property attaches a -view realisation to the respective interpreted -named graph by linking -instances of [<a href="#4.1.1_nrl:GraphView">nrl:GraphView</a>] -to respective instances of [<a href="#3.1.1._nrl:Graph">nrl:Graph</a>]. -In this way, it is always possible to determine which graph a -view is interpreting. Thus both the theoritical and the -practical separation between different interpretations of a named graph -and the original named -graph itself can be retained. As a result, it is always possible to -retrieve an original named graph, independently of how many views have -been applied over it.</p> - - - - -</div> - - - - -<h4 style="text-align: justify;"><a class="mozTocH4" name="mozTocId124884"></a><a name="4.1.3_nrl:hasSpecification"></a>4.1.3. -nrl:hasSpecification </h4> - - - - -<p>Views are realized according to a given view specification. -This -property determines the specification for a view by linking instances -of [<a href="#4.1.1_nrl:GraphView">nrl:GraphView</a>] -to instances of [<a href="#4.2.1._nrl:ViewSpecification">nrl:ViewSpecification</a>]. -View specifications are defined through instances of [<a href="#4.2.1._nrl:ViewSpecification">nrl:ViewSpecification</a>]. -This class, its subclasses, attributes and general characteristics are -introduced and defined in the following section. </p> - - - - -<h3 style="text-align: justify;"><a class="mozTocH3" name="mozTocId648959"></a><a name="4.2._View_Specification_Vocabulary"></a>4.2. -Views Specification Vocabulary</h3> - - - - -<div style="text-align: justify;"> -<p>This section presents -the vocabulary supporting graph view -specification. These specification are essentially the instructions to -how a view is to be -realized. -</p> - - - - -</div> - - - - -<h4 style="text-align: justify;"><a class="mozTocH4" name="mozTocId925367"></a><a name="4.2.1._nrl:ViewSpecification"></a>4.2.1. -nrl:ViewSpecification</h4> - - - - -<div style="text-align: justify;">This class represents a -view specification. Every graph view requires -an associated view specification. View specifications can take one of -two forms, modeled as the two subclasses [<a href="#4.2.3._nrl:RuleViewSpecification">nrl:RuleViewSpecification</a>] -and [<a href="#4.2.6._nrl:ExternalViewSpecification">nrl:ExternalViewSpecification</a>]. -The view specification defines the criteria for the realization of the -view. In the case of semantic views, view specifications also -state which semantics are realized through the [<a href="#4.2.2._nrl:realizes">nrl:realizes</a>] -property. -</div> - - - - -<h4 style="text-align: justify;"><a class="mozTocH4" name="mozTocId162918"></a><a name="4.2.2._nrl:realizes"></a>4.2.2. -nrl:realizes</h4> - - - - -<div style="text-align: justify;"> -<p>This property applies -only to subset of views introduced as semantic -views (see <a href="#4._Graph_Views_Extensions">Section -4</a> -introduction). It links a semantic view to the formal specifications of -the -semantics that it realizes. In effect this states that the view should -carry the realized, procedural semantics according to the given -semantics -definition, and not simply the implicit declarative -semantics. The overlap in <a href="#Fig4">Figure4</a> -and also in<a href="#Fig4"> </a><a href="#Fig1">Figure -1</a>) -between graph roles and views refers to these semantic views which -carry both procedural (through this property) and declarative -(through [<a href="#3.2.11._nrl:hasSemantics">nrl:hasSemantics</a>]) -semantics. This property should be distinguished from the [<a href="#3.2.11._nrl:hasSemantics">nrl:hasSemantics</a>] -property since this property has only a declarative role when it comes -to specifying the semantics for a graph.</p> - - - - -<span style="font-style: italic;"><span style="font-weight: bold;">Note:</span> </span>For NRL -to be -valid, all semantic views must carry both procedural and declarative -semantics. That is, any view (which can manifest itself also as a graph -role) that is linked to some semantics by [<a href="#4.2.2._nrl:realizes">nrl:realizes</a>], -should -also be linked to the same semantics by [<a href="#3.2.11._nrl:hasSemantics">nrl:hasSemantics</a>]. -This relationship between the two properties is not symmetric and it is -perfectly valid for a -graph role (that is not a view) to have only non-realized declarative -semantics. -</div> - - - - -<h4 style="text-align: justify;"><a class="mozTocH4" name="mozTocId266518"></a><a name="4.2.3._nrl:RuleViewSpecification"></a>4.2.3. -nrl:RuleViewSpecification </h4> - - - - -<div style="text-align: justify;">This class represents -one of the provided forms of view -specifications. Views can be specified by referring to a rule language -and a corresponding set of required rules within. The view is -subsequently realized by executing those rules, generating the -required output named graph. -The rule language and the selected rules are specified through the [<a href="#4.2.4._nrl:ruleLanguage">nrl:ruleLanguage</a>] -and [<a href="#4.2.5._nrl:rule">nrl:rule</a>] -properties, presented below.<br /> - - - - -</div> - - - - -<h4 style="text-align: justify;"><a class="mozTocH4" name="mozTocId718088"></a><a name="4.2.4._nrl:ruleLanguage"></a>4.2.4. -nrl:ruleLanguage</h4> - - - - -<p style="text-align: justify;">This property links a rule -view specification to the name of -the rule language supporting the required rules. The -rule language is -identified via a string referring to the language name.<br /> - - - - -</p> - - - - -<h4 style="text-align: justify;"><a class="mozTocH4" name="mozTocId518283"></a><a name="4.2.5._nrl:rule"></a>4.2.5. -nrl:rule</h4> - - - - -<p style="text-align: justify;">This property is used to -provide the actual rules -for a rule view -specification, with respect to the selected rule language. -The rules (or queries) are provided as a string.</p> - - - - -<h4 style="text-align: justify;"><a class="mozTocH4" name="mozTocId968780"></a><a name="4.2.6._nrl:ExternalViewSpecification"></a>4.2.6. -nrl:ExternalViewSpecification </h4> - - - - -<div style="text-align: justify;"> -<p>The second type of view -specification supported by NRL refers -to an external application, service or program -(external realizer) that automatically executes and returns the -required view without the need to select any rule or -language. The word -'external' refers to the fact that the actual view -specification is not given by instances of this class, but is -predefined within the external application. External view -specifications need only -specify the location of the external realizer through the -following property.</p> - - - - -</div> - - - - -<h4 style="text-align: justify;"><a class="mozTocH4" name="mozTocId745751"></a><a name="4.2.7._nrl:externalRealizer"></a>4.2.7. -nrl:externalRealizer</h4> - - - - -<div style="text-align: justify;"> -<p>External view -specifications rely on external realizers to realize a -particular view. An identifier for the external application, service or -program is assigned to the view specification through this property in -the form of -a string.</p> - - - - -</div> - - - - -<h3 style="text-align: justify;"><a class="mozTocH3" name="mozTocId227803"></a><a name="4.3_Graph_Views_Example"></a>4.3 -Graph Views Example</h3> - - - - -<div style="text-align: justify;"> -<p>The following example is -a continuation to that given in [<a href="#3.3._Named_Graph_Example">Section -.3</a>] and -it completes the dataflow diagram presented in the introduction [<a href="#Fig2">Figure 2</a>]. It -demonstrates how the -provided syntax supporting graph views can be used effectively. The -practical applicability of the introduced views is explained in more -detail in the introduction of the document and [<a href="#Fig2">Figure -2</a>].<br /> - - - - -</p> - - - - -[1] <span style="font-style: italic;">ex:kb2_metadata </span>states -that a new graph with the role of knowledge base, <span style="font-style: italic;">ex:kb2</span>, -is a graph view over graph<span style="font-style: italic;"> -ex:kb1 </span>defined in the example earlier<span style="font-style: italic;"> </span>according to a -view specification <span style="font-style: italic;">ex:rvs</span>. <br /> - - - - -<br /> - - - - -[2] <span style="font-style: italic;">ex:rvs</span> -is the view specification required to realize <span style="font-style: italic;">ex:kb2</span>. It is a -rule view specification, and it requires executing two rules -from the SPARQL language over the graph that <span style="font-style: italic;">ex:kb2</span> is -interpreting, namely <span style="font-style: italic;">ex:kb1</span>. The -view is defined as a semantic realizing view, which semantics -are given by <span style="font-style: italic;">ex:RDFSSemantics</span>.<br /> - - - - -<br /> - - - - -[3] <span style="font-style: italic;">ex:RDFSemantics </span>refers -to a document where the formal specification of the procedural -semantics realized by the view are given. These semantics are -identified by a label, <span style="font-style: italic;">RDFS</span>.<br /> - - - - -<br /> - - - - -[4] <span style="font-style: italic;">ex:kb3_metadata</span> -states that the graph <span style="font-style: italic;">ex:kb3 -</span>having role [<a href="#3.2.5._nrl:KnowledgeBase">nrl:KnowledgeBase</a>]<span style="font-style: italic;"> -</span>is a graph view over <span style="font-style: italic;">ex:kb2 </span>according -to a view specification <span style="font-style: italic;">ex:evs</span>. <br /> - - - - -<br /> - - - - -[5] The view specification for <span style="font-style: italic;">ex:kb3</span> -is defined to consist of an external view specification. This in -practice means that no specification is given in the graph definition, -but the virtual specification is assumed to be within the external -application or service that realizes the view. In this case, <span style="font-style: italic;">GraphTaxonomyExtractor </span>will -return the required realized view as the graph <span style="font-style: italic;">ex:kb3</span>.<br /> - - - - -<br /> - - - - -<table style="text-align: left; width: 100%;" border="1" cellpadding="2" cellspacing="2"> - - - - - <tbody> - - - - - <tr> - - - - - <td> <span style="font-family: monospace;"> @prefix nrl: -<http://www.semanticdesktop.org/ontology/yyyy/mm/dd/nrl#> -.</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - @prefix ex: -<http://www.example.org/vocabulary#> .</span><br style="font-family: monospace;" /> - - - - - <br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[1] -ex:kb2_metadata { </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ex:kb2 rdf:type nrl:KnowledgeBase , </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - nrl:GraphView ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - nrl:viewOn ex:kb1 -;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - nrl:hasSpecification ex:rvs . </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[2] ex:rvs -rdf:type nrl:RuleViewSpecification ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - nrl:realizes -ex:RDFSSemantics ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - nrl:ruleLanguage "SPARQL" ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - nrl:rule "CONSTRUCT {?s -?rdfs:subClassOf ?v} WHERE ..." ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - nrl:rule -"CONSTRUCT {?s ?rdf:type ?v} WHERE ..." . </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[3] -ex:RDFSSemantics rdf:type nrl:Semantics ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - nrl:semanticsDefinedBy -"http://www.w3.org/TR/2004/REC-rdf-mt-20040210/ ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - nrl:semanticsLabel "RDFS" . }</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[4] -ex:kb3_metadata {</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - ex:kb3 rdf:type nrl:GraphView ,</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - nrl:KnowledgeBase ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - - nrl:viewOn ex:kb2 ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - nrl:hasSpecification ex:evs -. </span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;">[5] ex:evs -rdf:type nrl:ExternalViewSpecification ;</span><br style="font-family: monospace;" /> - - - - - <span style="font-family: monospace;"> - nrl:externalRealizer -"GraphTaxonomyExtractor" . } </span></td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<br /> - - - - -</div> - - - - -<h2><a class="mozTocH2" name="mozTocId943672"></a><a name="5._Deprecated_Elements"></a>5. -Deprecated Elements</h2> - - - - -<p style="text-align: justify;"> In general -there are three criteria for -excluding -elements from NRL:</p> - - - - -<ol> - - - - - <li>Elements with no clear formal semantics.</li> - - - - - <li>Elements whose complexity cannot be handled.</li> - - - - - <li>Elements that are <span style="font-style: italic;">NEPOMUK -project</span>-specific.</li> - - - - - <li>Elements that do not belong to the Representation -Language -layer but rather to lower ontology levels.</li> - - - - - <li>Elements that have become redundant after introduction of -the NRL concepts.</li> - - - - -</ol> - - - - -<p style="text-align: justify;">The following is a list -of elements which have been -excluded -from NRL. Some of these elements might be moved to other NEPOMUK -ontologies, or removed completely. Given in the table are the -reasons why they have been excluded from this ontology, alongside the -resulting actions taken.</p> - - - - -<table style="width: 100%; height: 3496px;" id="table44" border="1"> - - - - - <tbody> - - - - - <tr> - - - - - <td style="text-align: justify;" width="20%">nrl:Thing</td> - - - - - <td style="text-align: justify;" width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" width="20%"> </td> - - - - - <td width="78%">The superclass of all conceptual -classes. See also [<a href="http://www.w3.org/TR/swbp-skos-core-spec/">SKOS -Concept</a>] -and [<a href="http://www.w3.org/TR/owl-guide/">OWL Thing</a>]</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">rdfs:Resource satisfies the -requirements for a top Resource representation.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Exclude.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:ResourceManifestation</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" width="20%"> </td> - - - - - <td width="78%">The superclass of all files or -web -resources. See also [<a href="http://www.w3.org/TR/2000/CR-rdf-schema-20000327/#s2.2.1">RDFS -Resource</a>]</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Distinction between abstract -resource and information resource not required at this level.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Move to upper-level -(foundational) -ontology.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:Association</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" width="20%"> </td> - - - - - <td width="78%">The superclass of n-ary -relations. -See also [<a href="http://www.topicmaps.org/xtm/#desc-association">Topic -Maps Association</a>]</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Not required at this level.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Move to upper-level -(foundational) -ontology.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:AssociationRole</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" width="20%"> </td> - - - - - <td width="78%">The superclass of relations for -N-ary associations. See also [<a href="http://www.topicmaps.org/xtm/#desc-association">Topic -Maps Association</a>]</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Not required at this level.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Move to upper-level -(foundational) -ontology.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:NRLClass</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" width="20%"> </td> - - - - - <td width="78%">The NRL's own class to enable -specific extensions.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">No specific restrictions in this -ontology requiring an extra class representation.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Move to -upper-level(foundational) -ontology if required.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:NRLProperty</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" width="20%"> </td> - - - - - <td width="78%">The NRL's own property to enable -specific extensions.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">No specific restrictions in this -ontology requiring an extra property representation.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Move to -upper-level(foundational) -ontology if required.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:DescribingProperty</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" width="20%"> </td> - - - - - <td width="78%">This class defines a class -instance -to be descriptive rather than relational. Descriptive properties cannot -have an inverse. See also [<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#DefiningProperties">OWL -DatatypeProperty</a>]</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Distinction between descriptive -and -relational properties not required at this level.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Move to upper-level -(foundational) -ontology.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:RelatingProperty</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" style="width: 20%;"> </td> - - - - - <td widdth="78%">This class defines a class -instance -to be relational rather than descriptive. Only relational properties -can have an inverse. See also [<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#DefiningProperties">OWL -ObjectProperty</a>]</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Distinction between descriptive -and -relational properties not required at this level.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Move to upper-level -(foundational) -ontology.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:hasNamespace</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" width="20%"> </td> - - - - - <td width="78%">Specifies the standard namespace -for -an ontology with particular attention to the hash or slash problem.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Not required at this level.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Move to Ontology Metadata Layer -provided semantics are clear.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:hasNamespaceAbbreviation</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" width="20%"> </td> - - - - - <td width="78%">Provides a means to specify the -standard abbreviation for an ontology's namespace.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Not required at this level.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Move to Ontology Metadata Layer -provided semantics are clear.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:isDefinedBy</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" width="20%"> </td> - - - - - <td width="78%">A standard for stating which -ontology defines a ontology element, to enable more efficient queries.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Not required at this level.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Move to Ontology Metadata Layer -provided semantics are clear.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:directType</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" width="20%"> </td> - - - - - <td width="78%">Specifies that a type is a -direct -type and not a type resulting from transitivity.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Not required since the -introduction of Graph Views.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Unclear</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:directSubClass</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" width="20%"> </td> - - - - - <td width="78%">Specifies a direct subclass of -some -class and not a subclass resulting from transitivity.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Not required since the -introduction of Graph Views.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Unclear</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:directSubProperty</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" width="20%"> </td> - - - - - <td width="78%">Specifies a direct subproperty -of -some property and not a subproperty resulting from transitivity.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Not required since the -introduction of Graph Views.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Unclear</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:altLabel</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" width="20%"> </td> - - - - - <td width="78%">The alternative labels for a -resource. A thesauri requirement in conjunction with [<a href="http://www.w3.org/TR/rdf-schema/#ch_label">rdfs:label</a>]. -See also [<a href="http://www.w3.org/TR/swbp-skos-core-spec/">skos:altLabel</a>]</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">This is an annotation property.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Move to annotation ontology.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:defaultValues</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" width="20%"> </td> - - - - - <td width="78%">The default value/s for a -property -assigned to instances of a class. Comparable to -Protégé's defaultValues slot attribute.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Not required at this level.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Move to general view ontology.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:hasPart</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" width="20%"> </td> - - - - - <td width="78%">This defines a resource as -having -a -subset resource. </td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">No clear formal semantics.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Exclude.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:partOf</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" width="20%"> </td> - - - - - <td width="78%">This defines a resource as being -a -subset of another. </td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">No clear formal semantics.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Exclude.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:hasTopic</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" width="20%"> </td> - - - - - <td width="78%">This states the topic of a -resource. -See also [<a href="http://www.w3.org/TR/swbp-skos-core-spec/">SKOS -isSubejctOf</a>]</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Not required at this level.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Move to annotation ontology.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:isTopicOf</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" width="20%"> </td> - - - - - <td width="78%">This states the resource -attributed -to a topic. See also [<a href="http://www.w3.org/TR/swbp-skos-core-spec/">SKOS -isSubjectOf</a>]</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Not required at this level.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Move to annotation ontology.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:occurrence</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" width="20%"> </td> - - - - - <td width="78%">This points to an instance of a -specific resource. See also [<a href="http://www.topicmaps.org/xtm/#desc-occurrence">Topic -Maps Occurences</a>] and [<a href="http://www.w3.org/TR/swbp-skos-core-spec/">SKOS -hasSubject</a>]</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">No formal semantics.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">Exclude.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="20%">nrl:isOccurenceOf</td> - - - - - <td width="78%"><i>Description</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td rowspan="5" style="width: 20%;"> </td> - - - - - <td width="78%">This points to a resource -classifying this and other similar instances. See also [<a href="http://www.topicmaps.org/xtm/#desc-occurrence">Topic -Maps Occurences</a>] and [<a href="http://www.w3.org/TR/swbp-skos-core-spec/">SKOS -hasSubject</a>]</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Reason</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%">No formal semantics.</td> - - - - - </tr> - - - - - <tr> - - - - - <td width="78%"><i>Action</i></td> - - - - - </tr> - - - - - <tr> - - - - - <td style="width: 100%;">Exclude.</td> - - - - - </tr> - - - - - - - - </tbody> -</table> - - - - -<h2><a class="mozTocH2" name="mozTocId225357"></a><a name="6._NRL_Semantics"></a>6. NRL -Semantics</h2> - - - - -<span style="font-style: italic;"><span style="font-weight: bold;">Note:</span> -The -Semantics of NRL will be formally specified at a later version of the -language.</span> -<dl> - - - - -</dl> - - - - -</div> - - - - -</div> - - - - -</div> - - - - -</div> - - - - -<div> -<h2><a class="mozTocH2" name="mozTocId501171"></a><a name="References"></a>References<br /> - - - - -</h2> - - - - -</div> - - - - -<span style="font-weight: bold;">[NAMED GRAPHS]</span> -<dl> - - - - - <dd><span style="font-weight: normal;"><a href="http://www2005.org/cdrom/docs/p613.pdf">Named Graphs, -Provenance and Trust</a>, </span><span style="font-weight: normal;">J. J. Carroll, C. Bizer, P. -Hayes and P. Stickler, Proceedings of WWW2005, May 2005, -Japan. </span></dd> - - - - - <dd><small><a style="font-family: Courier New,Courier,monospace;" href="http://www.w3.org/DesignIssues/Notation3">http://www.w3.org/2004/03/trix/</a></small><small><span style="font-family: Courier New;">.</span></small><span style="font-weight: bold;"></span><br /> - - - - - </dd> - - - - -</dl> - - - - -<div> -<dl> - - - - - <dt><span style="font-weight: bold;">[NOTATION3]</span></dt> - - - - - <dd><span style="font-weight: normal;"><a href="http://www.w3.org/DesignIssues/Notation3">A readable -language for data on the Web</a>. Tim Berners-Lee, Editor.</span></dd> - - - - - <dd><small><a style="font-family: Courier New,Courier,monospace;" href="http://www.w3.org/DesignIssues/Notation3">http://www.w3.org/DesignIssues/Notation3</a><span style="font-family: Courier New;"></span></small><small><span style="font-family: Courier New;">.</span></small><span style="font-weight: bold;"></span></dd> - - - - -</dl> - - - - -<dl> - - - - - <dt>[N-TRIPLES]<br /> - - - - - </dt> - - - - - <dd><cite></cite><a href="http://www.w3.org/TR/2004/REC-rdf-testcases-20040210/">N-Triples</a> -section in [<a href="#References">RDF -Specification - Tests</a>] </dd> - - - - -</dl> - - - - -<span style="font-weight: bold;">[OMV Report] -<br /> - - - - -</span> -<div style="margin-left: 40px;"><a href="http://ontoware.org/projects/omv/">Ontology Metadata -Vocabulary for the Semantic. Web</a>. Jens Hartmann (University -of Karlsruhe), Raul Palma (Universidad Politecnica de Madrid) and Elena -Paslaru Bontas (Free University of Berlin).<br /> - - - - -</div> - - - - -<div style="margin-left: 40px;"><small style="font-family: monospace;"><a href="http://ontoware.org/projects/omv/">http://ontoware.org/projects/omv/</a>.<br /> - - - - -<br /> - - - - -</small> -</div> - - - - -<span style="font-weight: bold;"> -[OWL -Overview] </span> -<div style="margin-left: 40px;"><cite></cite><a href="http://www.w3.org/TR/owl-features/">OWL -Web Ontology -Language Overview</a>.<cite> </cite>Deborah L. -McGuinness and Frank -van Harmelen, Editors, W3C Recommendation, 10 February 2004, <br /> - - - - -<small><span style="font-family: Courier New;"><a href="http://www.w3.org/TR/owl-features/">http://www.w3.org/TR/owl-features/</a>.</span></small><span style="font-weight: bold;"></span><br /> - - - - -</div> - - - - -<dl> - - - - - <dt>[RDF]</dt> - - - - - <dd><a href="http://www.w3.org/RDF/">Resource -Description Framework</a></dd> - - - - - <dt></dt> - - - - - <dt>[RDF Specification - PRIMER]</dt> - - - - - <dd><a href="http://www.w3.org/TR/rdf-primer/">RDF -Primer</a>, Frank Manola and Eric Miller, Editors, W3C -Recommendation, 10 February 2004, <font face="Courier New"> - <a href="http://www.w3.org/TR/2004/REC-rdf-primer-20040210/"><font size="2">http://www.w3.org/TR/2004/REC-rdf-primer-20040210/</font></a><font size="2">.</font></font></dd> - - - - - <dt></dt> - - - - - <dt>[RDF Specification - SYNTAX]</dt> - - - - - <dd><a href="http://www.w3.org/TR/rdf-syntax-grammar/">RDF/XML -Syntax Specification</a>, Dave Beckett, Editor, W3C -Recommendation, 10 February 2004, <font face="Courier New" size="2"> <a href="http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/"> -http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/</a>.</font></dd> - - - - - <dt></dt> - - - - - <dt>[RDF Specification - CONCEPTS]</dt> - - - - - <dd><a href="http://www.w3.org/TR/rdf-concepts/">Resource -Description Framework (RDF): Concepts and Abstract Syntax</a>, -Graham Klyne and Jeremy J. Carroll, Editors, W3C Recommendation, 10 -February 2004, </dd> - - - - - <dd><font face="Courier New" size="2"><a href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/">http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/</a>.</font></dd> - - - - - <dt></dt> - - - - - <dt>[RDF Specification - SEMANTICS]</dt> - - - - - <dd><a href="http://www.w3.org/TR/rdf-mt/">RDF -Semantics</a>, Patrick Hayes, Editor, W3C Recommendation, 10 -February 2004, <font face="Courier New" size="2"> <a href="http://www.w3.org/TR/2004/REC-rdf-mt-20040210/"> -http://www.w3.org/TR/2004/REC-rdf-mt-20040210/</a>.</font></dd> - - - - - <dt></dt> - - - - - <dt>[RDF Specification - MS]</dt> - - - - - <dd><a href="http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/">Resource -Description Framework (RDF) Model and Syntax</a>, W3C -Recommendation, 22 February 1999<br /> - - - - - <font face="Courier New" size="2"> <a href="http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/">http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/</a>.</font></dd> - - - - - <dt></dt> - - - - - <dt>[RDF Specification - TESTS]</dt> - - - - - <dd><a href="http://www.w3.org/TR/rdf-testcases/">RDF -Test Cases</a>, Jan Grant and Dave Beckett, Editors, W3C -Recommendation, 10 February 2004, <font face="Courier New" size="2"> <a href="http://www.w3.org/TR/2004/REC-rdf-testcases-20040210/"> -http://www.w3.org/TR/2004/REC-rdf-testcases-20040210/</a>.</font></dd> - - - - -</dl> - - - - -<dl> - - - - - <dt>[RDFS Specification]</dt> - - - - - <dd><a href="http://www.w3.org/TR/rdf-schema/">RDF -Vocabulary Description Language 1.0: RDF Schema</a>, Dan -Brickley, R.V. Guga, Brian McBride, W3C Recommendation, 10 February -2004, </dd> - - - - - <dd><font face="Courier New"><a href="http://www.w3.org/TR/2004/REC-rdf-primer-20040210/"><font size="2">http://www.w3.org/TR/2004/REC-rdf-primer-20040210/</font></a><font size="2">.</font></font></dd> - - - - -</dl> - - - - -<span style="font-weight: bold;">[SPARQL-QUERY]</span><cite><br /> - - - - -</cite> -<div style="margin-left: 40px;"><cite style="font-style: italic;"></cite><span style="font-style: italic;"></span><a href="http://www.w3.org/TR/2005/WD-rdf-sparql-query-20051123/">SPARQL -Query Language for RDF</a>, -E. Prud'hommeaux, A. Seaborne, Editors. World Wide Web Consortium. 23 -November 2005. Work in progress. This version is -http://www.w3.org/TR/2005/WD-rdf-sparql-query-20051123/. </div> - - - - -<div style="margin-left: 40px;"><small style="font-family: Courier New,Courier,monospace;"><a href="http://www.w3.org/TR/rdf-sparql-query/">http://www.w3.org/TR/rdf-sparql-query/</a></small><small><span style="font-family: Courier New;">.</span></small><br /> - - - - -</div> - - - - -<small style="font-weight: bold;"><span style="font-family: Courier New;"></span></small><br /> - - - - -<span style="font-weight: bold;">[TRIG]<br /> - - - - -</span> -<div style="margin-left: 40px;"><span style="font-weight: bold;"></span><small><span style="font-family: Courier New;"></span></small><a style="font-weight: normal;" href="http://www.wiwiss.fu-berlin.de/suhl/bizer/TriG/">TriG -Syntax</a><span style="font-weight: normal;">, Chris -Bizer, Freie Universität Berlin extends Turtle to serialise [<a href="#References">NAMED GRAPHS</a>] <br /> - - - - -</span><small><a style="font-family: monospace;" href="http://sites.wiwiss.fu-berlin.de/suhl/bizer/TriG/">http://sites.wiwiss.fu-berlin.de/suhl/bizer/TriG/</a></small><small><span style="font-family: Courier New;">.</span></small></div> - - - - -<span style="font-weight: bold;"></span><span style="font-weight: bold;"></span><span style="font-weight: bold;"></span><small><span style="font-family: Courier New;"></span></small><span style="font-weight: bold;"></span> -<dl> - - - - - <dt><span style="font-weight: bold;">[TURTLE]</span></dt> - - - - - <dd><a href="http://www.dajobe.org/2004/01/turtle/">Terse -- RDF Triple language</a>. Dave Beckett, Editor. 04 December 2004.</dd> - - - - - <dd><small><a style="font-family: monospace;" href="http://www.dajobe.org/2004/01/turtle/">http://www.dajobe.org/2004/01/turtle/</a></small><small><span style="font-family: Courier New;">.</span></small></dd> - - - - - <dt></dt> - - - - -</dl> - - - - -<hr style="width: 100%; height: 2px;" /><span style="font-family: Courier New;"></span> -<dl> - - - - - <dd> - - - - <dl> - - - - - - - - </dl> - - - - - </dd> - - - - -</dl> - - - - -</div> |