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748 lines
28 KiB
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<title>RDF Interest Group: discussion note: RDF Model Summary</title>
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<style type="text/css">
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.EXAMPLE { margin-left: 1em }
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</style>
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</head>
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<body text="#000000" bgcolor="#FFFFFF">
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<h2 align="right">Strawman: RDF-Model-Summary-1</h2>
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<h1>Resource Description Framework: Data Model Summary</h1>
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<h3>RDF Interest Group Discussion Document</h3>
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<dl>
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<dt>This Version:</dt>
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<dd><a href="/2000/09/rdfmodel/1">
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http://www.w3.org/2000/09/rdfmodel/1</a> $Date: 2000/09/08 13:45:48 $<br />
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</dd>
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<dt>Newest Version:</dt>
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<dd><a href="/2000/09/rdfmodel/">
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http://www.w3.org/2000/09/rdfmodel/</a><br />
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</dd>
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<dt>Editor (butcher ;-):</dt>
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<dd>Dan Brickley <tt><a href="mailto:danbri@w3.org">
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<danbri@w3.org></a>, World Wide Web Consortium /
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ILRT</tt></dd>
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<dt>Rather crudely derrived from <a href=
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"http://www.w3.org/TR/REC-rdf-syntax/">REC-rdf-syntax-19990222</a>,
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whose editors were:</dt>
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<dd>Ora Lassila <tt><a href=
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"mailto:ora.lassila@research.nokia.com">
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<ora.lassila@research.nokia.com></a></tt>, Nokia Research
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Center<br />
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Ralph R. Swick <tt><a href="mailto:swick@w3.org">
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<swick@w3.org></a></tt>, World Wide Web Consortium</dd>
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</dl>
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<p><font size="-1"><a href=
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"http://www.w3.org/Consortium/Legal/ipr-notice.html#Copyright">
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Copyright</a> © 1997,1998,1999,2000 <a href=
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"http://www.w3.org">W3C</a> (<a href=
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"http://www.lcs.mit.edu">MIT</a>, <a href="http://www.inria.fr/">
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INRIA</a>, <a href="http://www.keio.ac.jp/">Keio</a> ), All Rights
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Reserved. W3C <a href=
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"http://www.w3.org/Consortium/Legal/ipr-notice.html#LegalDisclaimer">
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liability,</a> <a href=
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"http://www.w3.org/Consortium/Legal/ipr-notice.html#W3CTrademarks">
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trademark</a>, <a href=
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"http://www.w3.org/Consortium/Legal/copyright-documents.html">
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document use</a> and <a href=
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"http://www.w3.org/Consortium/Legal/copyright-software.html">
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software licensing</a> rules apply.</font></p>
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<h2>Status of This Document</h2>
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<p><strong>Important:</strong> this document should <em>not</em> be
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mistaken for a W3C Specification. The text below was crudely
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excerpted from the <a href=
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"http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/">RDF Model and
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Syntax REC</a>. Unlike that document, this current text is not a
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complete work.</p>
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<p>This document has been prepared (solely as a personal contribution by
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the editor) as a strawman discussion
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document for consideration by the <a href="/RDF/Interest/">RDF
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Interest Group</a>.
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</p>
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<p>It was produced by taking the RDF Model and
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Syntax specification and removing most of the content that relates
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to the RDF 1.0 XML grammar, examples, and other material not
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directly relevant to the specification of the RDF data model. It
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should be noted that the initial version of this excerpted 'RDF
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Model Overview' was <em>not</em> produced with any great attention
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to detail, and serves solely as a 'proof of concept' or strawman
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sketch.</p>
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<p><strong>RDF implementors health warning</strong>: please don't
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use this work as a reference document, tempting as it may be. The
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sole use for this is to futher the <a href=
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"http://lists.w3.org/Archives/Public/www-rdf-interest/2000Sep/0066.html">
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discussion</a> on www-rdf-interest and refine the <a href=
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"/2000/03/rdf-tracking/">RDF Issues List</a>. It should also be emphasised
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that no commitment to any ongoing
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maintainance or refinement of this document has been made.
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</p>
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<p>Comments on this discussion document may be sent to <<a href=
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"mailto:www-rdf-interest@w3.org">www-rdf-interest@w3.org</a>>,
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the mailing list of the <a href="/RDF/Interest/">RDF Interest
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Group</a>.</p>
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<hr width="100%" />
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<h2><a id="TOC" name="TOC"></a>Table of Contents</h2>
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<ol>
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<li><a href="#intro">Introduction</a></li>
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<li><a href="#basic">Basic RDF Model</a></li>
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<li><a href="#container">RDF containers</a></li>
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<li><a href="#statements">RDF statements</a></li>
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<li><a href="#model">Formal Model for RDF</a></li>
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<li><a href="#glossary">Glossary</a></li>
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<li><a href="#references">Appendix: References</a></li>
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</ol>
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<hr width="100%" />
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<h2><a id="intro" name="intro"></a>1. Introduction</h2>
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<p>The World Wide Web was originally built for human consumption,
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and although everything on it is <i>machine-readable</i>, this data
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is not <i>machine-understandable</i>. It is very hard to automate
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anything on the Web, and because of the volume of information the
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Web contains, it is not possible to manage it manually. The
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solution proposed here is to use <i>metadata</i> to describe the
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data contained on the Web. Metadata is "data about data" (for
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example, a library catalog is metadata, since it describes
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publications) or specifically in the context of this specification
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"data describing Web resources". The distinction between "data" and
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"metadata" is not an absolute one; it is a distinction created
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primarily by a particular application, and many times the same
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resource will be interpreted in both ways simultaneously.</p>
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<a id="basic" name="basic"></a>
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<h2>2. Basic RDF Model</h2>
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<p>The foundation of RDF is a model for representing named
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properties and property values. The RDF model draws on
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well-established principles from various data representation
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communities. RDF properties may be thought of as attributes of
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resources and in this sense correspond to traditional
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attribute-value pairs. RDF properties also represent relationships
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between resources and an RDF model can therefore resemble an
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entity-relationship diagram. (More precisely, RDF Schemas —
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which are themselves instances of RDF data models — are ER
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diagrams.) In object-oriented design terminology, resources
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correspond to objects and properties correspond to instance
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variables.</p>
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<p>The RDF data model is a syntax-neutral way of representing RDF
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expressions. The data model representation is used to evaluate
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equivalence in meaning. Two RDF expressions are equivalent if and
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only if their data model representations are the same. This
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definition of equivalence permits some syntactic variation in
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expression without altering the meaning. (See <a href=
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"#stringComparison">Section 6.</a> for additional discussion of
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string comparison issues.)</p>
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<p>The basic data model consists of three object types:</p>
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<table width="90%" summary="presentational table">
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<tr valign="top">
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<td><a id="resource" name="resource"></a>Resources</td>
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<td>All things being described by RDF expressions are called <i>
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resources</i>. A resource may be an entire Web page; such as the
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HTML document "http://www.w3.org/Overview.html" for example. A
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resource may be a part of a Web page; e.g. a specific HTML or XML
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element within the document source. A resource may also be a whole
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collection of pages; e.g. an entire Web site. A resource may also
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be an object that is not directly accessible via the Web; e.g. a
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printed book. Resources are always named by URIs plus optional
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anchor ids (see [<a href=
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"http://www.ietf.org/internet-drafts/draft-fielding-uri-syntax-04.txt">
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URI</a>]). Anything can have a URI; the extensibility of URIs
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allows the introduction of identifiers for any entity
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imaginable.</td>
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</tr>
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<tr valign="top">
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<td><a id="propertyType" name="propertyType"></a><a id="property"
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name="property"></a>Properties</td>
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<td>A <i>property</i> is a specific aspect, characteristic,
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attribute, or relation used to describe a resource. Each property
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has a specific meaning, defines its permitted values, the types of
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resources it can describe, and its relationship with other
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properties. This document does not address how the characteristics
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of properties are expressed; for such information, refer to the <a
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href="/TR/1998/WD-rdf-schema">RDF Schema specification</a>).</td>
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</tr>
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<tr valign="top">
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<td><a id="statement" name="statement">
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</a>Statements </td>
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<td>A specific resource together with a named property plus the
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value of that property for that resource is an RDF <i>
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statement</i>. These three individual parts of a statement are
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called, respectively, the <i>subject</i>, the <i>predicate</i>, and
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the <i>object</i>. The object of a statement (i.e., the property
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value) can be another resource or it can be a literal; i.e., a
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resource (specified by a URI) or a simple string or other primitive
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datatype defined by XML. In RDF terms, a <i>literal</i> may have
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content that is XML markup but is not further evaluated by the RDF
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processor. There are some syntactic restrictions on how markup in
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literals may be expressed; see <a href="#quoting">Section
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2.2.1.</a></td>
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</tr>
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</table>
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<a name="container" id="container"></a>
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<h2>3. Container Model</h2>
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<p>RDF defines three types of container objects:</p>
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<table width="90%" summary="presentational table">
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<tr valign="top">
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<td><a id="Bag" name="Bag"></a>Bag</td>
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<td>An unordered list of resources or literals. <i>Bag</i>s are
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used to declare that a property has multiple values and that there
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is no significance to the order in which the values are given. <i>
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Bag</i> might be used to give a list of part numbers where the
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order of processing the parts does not matter. Duplicate values are
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permitted.</td>
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</tr>
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<tr valign="top">
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<td><a id="Sequence" name="Sequence"></a>Sequence</td>
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<td>An ordered list of resources or literals. <i>Sequence</i> is
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used to declare that a property has multiple values and that the
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order of the values is significant. <i>Sequence</i> might be used,
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for example, to preserve an alphabetical ordering of values.
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Duplicate values are permitted.</td>
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</tr>
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<tr valign="top">
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<td><a id="Alternative" name="Alternative">
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</a>Alternative </td>
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<td>A list of resources or literals that represent alternatives for
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the (single) value of a property. <i>Alternative</i> might be used
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to provide alternative language translations for the title of a
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work, or to provide a list of Internet mirror sites at which a
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resource might be found. An application using a property whose
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value is an <i>Alternative</i> collection is aware that it can
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choose any one of the items in the list as appropriate.</td>
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</tr>
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</table>
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<blockquote><i>Note: The definitions of</i> Bag <i>and</i> Sequence
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<i>explicitly permit duplicate values. RDF does not define a core
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concept of</i> Set<i>, which would be a</i> Bag <i>with no
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duplicates, because the RDF core does not mandate an enforcement
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mechanism in the event of violations of such constraints. Future
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work layered on the RDF core may define such
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facilities.</i></blockquote>
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<p>To represent a collection of resources, RDF uses an additional
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resource that identifies the specific collection (an <i>
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instance</i> of a collection, in object modeling terminology). This
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resource must be declared to be an instance of one of the container
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object types defined above. The <i>type</i> property, defined
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below, is used to make this declaration. The membership relation
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between this container resource and the resources that belong in
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the collection is defined by a set of properties defined expressly
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for this purpose. These membership properties are named simply
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"_1", "_2", "_3", etc. Container resources may have other
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properties in addition to the membership properties and the <i>
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type</i> property. Any such additional statements describe the
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container; see <a href="#distributedReferents">Section 3.3</a>,
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Distributive Referents, for discussion of statements about each of
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the members themselves.</p>
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<p>A common use of containers is as the value of a property. When
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used in this way, the statement still has a single statement object
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regardless of the number of members in the container; the container
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resource itself is the object of the statement.</p>
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<a name="statements" id="statements"></a> <a id="higherorder" name=
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"higherorder"></a>
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<h2>4. Modeling Statements and Statements about Statements</h2>
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<p>In addition to making statements about Web resources, RDF can be
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used for making statements about other RDF statements; we will
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refer to these as <i>higher-order statements</i>. In order to make
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a statement about another statement, we actually have to build a
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model of the original statement; this model is a new resource to
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which we can attach additional properties.</p>
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<p>Statements are made about resources. A model of a statement is
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the resource we need in order to be able to make new statements
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(higher-order statements) about the modeled statement.</p>
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<p>For example, let us consider the sentence</p>
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<blockquote><i>Ora Lassila is the creator of the resource
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http://www.w3.org/Home/Lassila.</i></blockquote>
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<p>RDF would regard this sentence as a fact. If, instead, we write
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the sentence</p>
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<blockquote><i>Ralph Swick says that Ora Lassila is the creator of
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the resource http://www.w3.org/Home/Lassila.</i></blockquote>
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<p>we have said nothing about the resource
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http://www.w3.org/Home/Lassila; instead, we have expressed a fact
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about a statement Ralph has made. In order to express this fact to
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RDF, we have to model the original statement as a resource with
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four properties. This process is formally called <i>reification</i>
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in the Knowledge Representation community. A model of a statement
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is called a <i>reified statement</i>.</p>
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<p>To model statements RDF defines the following properties:</p>
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<table width="90%" summary="presentational table">
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<tr>
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<td valign="top"><a id="propObj" name="propObj"></a><a id="subject"
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name="subject"></a>subject</td>
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<td>The <i>subject</i> property identifies the resource being
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described by the modeled statement; that is, the value of the <i>
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subject</i> property is the resource about which the original
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statement was made (in our example,
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http://www.w3.org/Home/Lassila).</td>
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</tr>
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<tr>
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<td valign="top"><a id="propName" name="propName"></a><a id=
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"predicate" name="predicate"></a>predicate </td>
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<td>The <i>predicate</i> property identifies the original property
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in the modeled statement. The value of the <i>predicate</i>
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property is a resource representing the specific property in the
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original statement (in our example, creator).</td>
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</tr>
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<tr>
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<td valign="top"><a id="value" name="value"></a><a id="object"
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name="object"></a>object</td>
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<td>The <i>object</i> property identifies the property value in the
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modeled statement. The value of the <i>object</i> property is the
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object in the original statement (in our example, "Ora
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Lassila").</td>
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</tr>
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<tr>
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<td valign="top"><a id="instanceOf" name="instanceOf"></a><a id=
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"type" name="type"></a>type </td>
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<td>The value of the <i>type</i> property describes the type of the
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new resource. All reified statements are instances of
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RDF:Statement; that is, they have a <i>type</i> property whose
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object is RDF:Statement. The <i>type</i> property is also used more
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generally to declare the type of any resource, as was shown in
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Section 3, "Containers".</td>
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</tr>
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</table>
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<p>A new resource with the above four properties represents the
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original statement and can both be used as the object of other
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statements and have additional statements made about it. The
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resource with these four properties is not a replacement for the
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original statement, it is a model of the statement. A statement and
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its corresponding reified statement exist independently in an RDF
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graph and either may be present without the other. The RDF graph is
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said to contain the fact given in the statement if and only if the
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statement is present in the graph, irrespective of whether the
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corresponding reified statement is present.</p>
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<p>To model the example above, we could attach another property to
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the reified statement (say, "attributedTo") with an appropriate
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value (in this case, "Ralph Swick").</p>
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<p>...</p>
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<p>Reification is also needed to represent explicitly in the model
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the statement grouping implied by <tt>Description</tt> elements.
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The RDF graph model does not need a special construct for <tt>
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Description</tt>s; since <tt>Description</tt>s really are
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collections of statements, a <tt>Bag</tt> container is used to
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indicate that a set of statements came from the same (syntactic)
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<tt>Description</tt>. Each statement within a <tt>Description</tt>
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is reified and each of the reified statements is a member of the
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Bag representing that <tt>Description</tt>. As an example, the RDF
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fragment</p>
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<h2><a id="model" name="model"></a>5. Formal Model for RDF</h2>
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<p>The RDF Model and Syntax specification shows three
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representations of the data model; as 3-tuples (triples), as a
|
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graph, and in XML. These representations have equivalent meaning.
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|
The mapping between the representations used in this specification
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|
is not intended to constrain in any way the internal representation
|
|
used by implementations.</p>
|
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<p>The RDF data model is defined formally as follows:</p>
|
|
|
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<table border="1" width="90%" summary="presentational table">
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<tr>
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<td>
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<ol>
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<li>There is a set called <i>Resources</i>.</li>
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<li>There is a set called <i>Literals</i>.</li>
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<li>There is a subset of <i>Resources</i> called <i>
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Properties</i>.</li>
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<li><a id="triple" name="triple"></a>There is a set called <i>
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Statements</i>, each element of which is a triple of the form
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<p>{pred, sub, obj}</p>
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<p>Where pred is a property (member of <i>Properties</i>), sub is a
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resource (member of <i>Resources</i>), and obj is either a resource
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or a literal (member of <i>Literals</i>).</p>
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</li>
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</ol>
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</td>
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</tr>
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</table>
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<p>We can view a set of statements (members of <i>Statements</i>)
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as a directed labeled graph: each resource and literal is a vertex;
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a triple {p, s, o} is an arc from s to o, labeled by p. This is
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illustrated in figure 11.</p>
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<center>
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<p><img src="fig11.gif" alt="statement graph template" /><a href=
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"fig11.html">D</a></p>
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|
</center>
|
|
|
|
<center>
|
|
<p>Figure 11: Simple statement graph template</p>
|
|
</center>
|
|
|
|
<p>This can be read either</p>
|
|
|
|
<blockquote><i>o is the value of p for s</i></blockquote>
|
|
|
|
<p>or (left to right)</p>
|
|
|
|
<blockquote><i>s has a property p with a value o</i></blockquote>
|
|
|
|
<p>or even</p>
|
|
|
|
<blockquote><i>the p of s is o</i></blockquote>
|
|
|
|
<p>For example, the sentence</p>
|
|
|
|
<blockquote><i>Ora Lassila is the creator of the resource
|
|
http://www.w3.org/Home/Lassila</i></blockquote>
|
|
|
|
<p>would be represented graphically as follows:</p>
|
|
|
|
<center>
|
|
<p><img src="fig12.gif" alt="Simple statement graph" /><a href=
|
|
"fig12.html">D</a></p>
|
|
</center>
|
|
|
|
<center>
|
|
<p>Figure 12: Simple statement graph</p>
|
|
</center>
|
|
|
|
<p>and the corresponding triple (member of <i>Statements</i>) would
|
|
be</p>
|
|
|
|
<blockquote>{creator, [http://www.w3.org/Home/Lassila], "Ora
|
|
Lassila"}</blockquote>
|
|
|
|
<p>The notation [<i>I</i>] denotes the resource identified by the
|
|
URI <i>I</i> and quotation marks denote a literal.</p>
|
|
|
|
<p>Using the triples, we can explain how statements are reified (as
|
|
introduced in Section 4). Given a statement</p>
|
|
|
|
<blockquote>{creator, [http://www.w3.org/Home/Lassila], "Ora
|
|
Lassila"}</blockquote>
|
|
|
|
<p>we can express the reification of this as a new resource X as
|
|
follows:</p>
|
|
|
|
<blockquote>{type, [X], [RDF:Statement]}<br />
|
|
{predicate, [X], [creator]}<br />
|
|
{subject, [X], [http://www.w3.org/Home/Lassila]}<br />
|
|
{object, [X], "Ora Lassila"}</blockquote>
|
|
|
|
<p>From the standpoint of an RDF processor, facts (that is,
|
|
statements) are triples that are members of <i>Statements</i>.
|
|
Therefore, the original statement remains a fact despite it being
|
|
reified since the triple representing the original statement
|
|
remains in <i>Statements</i>. We have merely added four more
|
|
triples.</p>
|
|
|
|
<p>The property named "type" is defined to provide primitive
|
|
typing. The formal definition of type is:</p>
|
|
|
|
<a id="formalType" name="formalType"></a>
|
|
|
|
<table border="1" width="90%" summary="presentational table">
|
|
<tr>
|
|
<td>
|
|
<ol start="5">
|
|
<li>There is an element of <i>Properties</i> known as
|
|
RDF:type.</li>
|
|
|
|
<li>Members of <i>Statements</i> of the form {RDF:type, sub, obj}
|
|
must satisfy the following: sub and obj are members of <i>
|
|
Resources.</i> [<a href="/TR/1998/WD-rdf-schema">RDFSchema</a>]
|
|
places additional restrictions on the use of type.</li>
|
|
</ol>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
<p>Furthermore, the formal specification of reification is:</p>
|
|
|
|
<a id="formalReification" name="formalReification"></a>
|
|
|
|
<table border="1" width="90%" summary="presentational table">
|
|
<tr>
|
|
<td>
|
|
<ol start="7">
|
|
<li>There is an element of <i>Resources</i>, not contained in <i>
|
|
Properties</i>, known as RDF:Statement.</li>
|
|
|
|
<li>There are three elements in <i>Properties</i> known as
|
|
RDF:predicate, RDF:subject and RDF:object.</li>
|
|
|
|
<li>Reification of a triple {pred, sub, obj} of <i>Statements</i>
|
|
is an element r of <i>Resources</i> representing the reified triple
|
|
and the elements s<sub>1</sub>, s<sub>2</sub>, s<sub>3</sub>, and
|
|
s<sub>4</sub> of <i>Statements</i> such that
|
|
|
|
<p>s<sub>1</sub>: {RDF:predicate, r, pred}<br />
|
|
s<sub>2</sub>: {RDF:subject, r, subj}<br />
|
|
s<sub>3</sub>: {RDF:object, r, obj}<br />
|
|
s<sub>4</sub>: {RDF:type, r, [RDF:Statement]}</p>
|
|
</li>
|
|
</ol>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
<p>The resource r in the definition above is called the <i>reified
|
|
statement</i>. When a resource represents a reified statement; that
|
|
is, it has an RDF:type property with a value of RDF:Statement, then
|
|
that resource must have exactly one RDF:subject property, one
|
|
RDF:object property, and one RDF:predicate property.</p>
|
|
|
|
<p>As described in Section 3, it is frequently necessary to
|
|
represent a collection of resources or literals; for example to
|
|
state that a property has an ordered sequence of values. RDF
|
|
defines three kinds of collections: ordered lists, called <i>
|
|
Sequences</i>, unordered lists, called <i>Bags</i>, and lists that
|
|
represent alternatives for the (single) value of a property, called
|
|
<i>Alternatives</i>.</p>
|
|
|
|
<p>Formally, these three collection types are defined by:</p>
|
|
|
|
<a id="formalCollection" name="formalCollection"></a>
|
|
|
|
<table border="1" width="90%" summary="presentational table">
|
|
<tr>
|
|
<td>
|
|
<ol start="10">
|
|
<li>There are three elements of <i>Resources</i>, not contained in
|
|
<i>Properties</i>, known as RDF:Seq, RDF:Bag, and RDF:Alt.</li>
|
|
|
|
<li>There is a subset of <i>Properties</i> corresponding to the
|
|
ordinals (1, 2, 3, ...) called <i>Ord</i>. We refer to elements of
|
|
<i>Ord</i> as RDF:_1, RDF:_2, RDF:_3, ...</li>
|
|
</ol>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
<p>To represent a collection <i>c</i>, create a triple {RDF:type,
|
|
<i>c</i>, <i>t</i>} where <i>t</i> is one of the three collection
|
|
types RDF:Seq, RDF:Bag, or RDF:Alt. The remaining triples {RDF:_1,
|
|
<i>c</i>, <i>r</i><sub>1</sub>}, ..., {RDF:_n, <i>c</i>, <i>
|
|
r</i><sub>n</sub>}, ... point to each of the members <i>
|
|
r</i><sub>n</sub> of the collection. For a single collection
|
|
resource there may be at most one triple whose predicate is any
|
|
given element of <i>Ord</i> and the elements of <i>Ord</i> must be
|
|
used in sequence starting with RDF:_1. For resources that are
|
|
instances of the RDF:Alt collection type, there must be exactly one
|
|
triple whose predicate is RDF:_1 and that is the default value for
|
|
the Alternatives resource (that is, there must always be at least
|
|
one alternative).</p>
|
|
|
|
<a id="glossary" name="glossary"></a>
|
|
|
|
<h2>Glossary</h2>
|
|
|
|
<dl>
|
|
<dt>Arc</dt>
|
|
|
|
<dd>A representation of a property in a graph form; specifically
|
|
the edges in a directed labeled graph.</dd>
|
|
|
|
<dt>Attribute</dt>
|
|
|
|
<dd>A characteristic of an object. In Chapter 6 this term refers to
|
|
a specific XML syntactic construct; the <tt>name="value"</tt>
|
|
portions of an XML tag.</dd>
|
|
|
|
<dt>Element</dt>
|
|
|
|
<dd>As used here, this term refers to a specific XML syntactic
|
|
construct; i.e., the material between matching XML start and end
|
|
tags.</dd>
|
|
|
|
<dt>Literal</dt>
|
|
|
|
<dd>The most primitive value type represented in RDF, typically a
|
|
string of characters. The content of a literal is not interpreted
|
|
by RDF itself and may contain additional XML markup. Literals are
|
|
distinguished from Resources in that the RDF model does not permit
|
|
literals to be the subject of a statement.</dd>
|
|
|
|
<dt>Node</dt>
|
|
|
|
<dd>A representation of a resource or a literal in a graph form;
|
|
specifically, a vertex in a directed labeled graph.</dd>
|
|
|
|
<dt><a href="#property">Property</a></dt>
|
|
|
|
<dd>A specific attribute with defined meaning that may be used to
|
|
describe other resources. A property plus the value of that
|
|
property for a specific resource is a <i>statement</i> about that
|
|
resource. A property may define its permitted values as well as the
|
|
types of resources that may be described with this property.</dd>
|
|
|
|
<dt><a href="#resource">Resource</a></dt>
|
|
|
|
<dd>An abstract object that represents either a physical object
|
|
such as a person or a book or a conceptual object such as a color
|
|
or the class of things that have colors. Web pages are usually
|
|
considered to be physical objects, but the distinction between
|
|
physical and conceptual or abstract objects is not important to
|
|
RDF. A resource can also be a component of a larger object; for
|
|
example, a resource can represent a specific person's left hand or
|
|
a specific paragraph out of a document. As used in this
|
|
specification, the term resource refers to the whole of an object
|
|
if the URI does not contain a fragment (anchor) id or to the
|
|
specific subunit named by the fragment or anchor id.</dd>
|
|
|
|
<dt><a href="#statement">Statement</a></dt>
|
|
|
|
<dd>An expression following a specified grammar that names a
|
|
specific resource, a specific property (attribute), and gives the
|
|
value of that property for that resource. More specifically here,
|
|
an <i>RDF statement</i> is a statement using the RDF/XML grammar
|
|
specified in this document.</dd>
|
|
|
|
<dt><a href="#triple">Triple</a></dt>
|
|
|
|
<dd>A representation of a statement used by RDF, consisting of just
|
|
the property, the resource identifier, and the property value in
|
|
that order.</dd>
|
|
</dl>
|
|
|
|
<h2><a id="references" name="references"></a>Appendix:
|
|
References</h2>
|
|
|
|
<dl>
|
|
<dt>[Dexter94]</dt>
|
|
|
|
<dd>F. Halasz and M. Schwarz. The Dexter Hypertext Reference Model.
|
|
Communications of the ACM, 37(2):30--39, February 1994. Edited by
|
|
K. Grønbæck and R. Trigg. <a href=
|
|
"http://www.acm.org/pubs/citations/journals/cacm/1994-37-2/p30-halasz/">
|
|
http://www.acm.org/pubs/citations/journals/cacm/1994-37-2/p30-halasz/</a></dd>
|
|
|
|
<dt>[HTML]</dt>
|
|
|
|
<dd>HTML 4.0 Specification, Raggett, Le Hors, Jacobs eds, World
|
|
Wide Web Consortium Recommendation; <a href=
|
|
"http://www.w3.org/TR/REC-html40/">
|
|
http://www.w3.org/TR/REC-html40</a></dd>
|
|
|
|
<dt>[ISO10646]</dt>
|
|
|
|
<dd>ISO/IEC 10646. The applicable version of this standard is
|
|
defined in the XML specification [<a href=
|
|
"/TR/REC-xml">XML</a>].</dd>
|
|
|
|
<dt>[NAMESPACES]</dt>
|
|
|
|
<dd>Namespaces in XML; Bray, Hollander, Layman eds, World Wide Web
|
|
Consortium Recommendation; <a href=
|
|
"http://www.w3.org/TR/1999/REC-xml-names-19990114">
|
|
http://www.w3.org/TR/1999/REC-xml-names-19990114</a>.</dd>
|
|
|
|
<dt>[PICS]</dt>
|
|
|
|
<dd>PICS Label Distribution Label Syntax and Communication
|
|
Protocols, Version 1.1, W3C Recommendation 31-October-96; <a href=
|
|
"http://www.w3.org/TR/REC-PICS-labels">
|
|
http://www.w3.org/TR/REC-PICS-labels</a>.</dd>
|
|
|
|
<dt>[RDFSchema]</dt>
|
|
|
|
<dd>Resource Description Framework (RDF) Schemas; Brickley, Guha,
|
|
Layman eds., World Wide Web Consortium Working Draft; <a href=
|
|
"/TR/1998/WD-rdf-schema">
|
|
http://www.w3.org/TR/1998/WD-rdf-schema</a></dd>
|
|
|
|
<dt><a id="rfc2119" name="rfc2119"></a>[RFC2119]</dt>
|
|
|
|
<dd>Key words for use in RFCs to Indicate Requirement Levels; S.
|
|
Bradner, March 1997; <a href=
|
|
"http://www.isi.edu/in-notes/rfc2119.txt">RFC2119</a>.</dd>
|
|
|
|
<dt>[Unicode]</dt>
|
|
|
|
<dd>The Unicode Standard. The applicable version of this standard
|
|
is the version defined by the XML specification [<a href=
|
|
"/TR/REC-xml">XML</a>].</dd>
|
|
|
|
<dt>[URI]</dt>
|
|
|
|
<dd>Uniform Resource Identifiers (URI): Generic Syntax;
|
|
Berners-Lee, Fielding, Masinter, Internet Draft Standard August,
|
|
1998; <a href="http://www.isi.edu/in-notes/rfc2396.txt">
|
|
RFC2396</a>.</dd>
|
|
|
|
<dt>[XML]</dt>
|
|
|
|
<dd>Extensible Markup Language (XML) 1.0; World Wide Web Consortium
|
|
Recommendation; <a href="http://www.w3.org/TR/REC-xml">
|
|
http://www.w3.org/TR/REC-xml</a>.</dd>
|
|
|
|
<dt>[XMLinHTML]</dt>
|
|
|
|
<dd>XML in HTML Meeting Report; Connolly, Wood eds.; World Wide Web
|
|
Consortium Note; <a href="http://www.w3.org/TR/NOTE-xh">
|
|
http://www.w3.org/TR/NOTE-xh</a>.</dd>
|
|
</dl>
|
|
|
|
<hr />
|
|
</body>
|
|
</html>
|
|
|