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276 lines
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276 lines
12 KiB
<?xml version="1.0"?>
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<!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>A Semantic Web Language (Swell)</title>
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<meta http-equiv="Content-Type" content="text/html" />
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</head>
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<body>
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<p><a href="../../">W3C</a> <a href="../07/hs78/Overview.html">Toward
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Swell</a></p>
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<h1>Toward Swell, the Semantic Web Logic Language</h1>
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<address>
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status: originally sketched just before a 6 Jul meeting; integrating into <a
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href="../07/hs78/Overview.html">more swell stuff</a> before a 19-20 July
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meeting<br />
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<a href="http://www.w3.org/People/Connolly/">Dan Connolly</a><br />
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<small>$Revision: 1.15 $ of $Date: 2000/07/27 00:52:57 $ by $Author:
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connolly $</small>
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</address>
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<ol>
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<li>the basic RDF statement model: subject, predicate, and object
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<ul>
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<li>demo: show a few items of shoe instance data converted to RDF in the
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<a href="http://www.w3.org/2000/04shoe-swell/">Shoe->RDF stuff</a>
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<ul>
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<li><strong>issue</strong>: symbols (URIs) vs. literals (<a
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href="http://lists.w3.org/Archives/Public/www-rdf-interest/2000May/0090.html">21
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May gotcha report</a>)</li>
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</ul>
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</li>
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<li>using XSLT to harvest facts:
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<ul>
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<li><a href="http://www.w3.org/2000/07/hs78/dc-extract/form">dublin
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core service</a>, <a
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href="http://www.w3.org/2000/07/hs78/foaf">foaf</a>/homepage/events
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stuff@@</li>
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<li>using <a
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href="http://www.w3.org/2000/07/hs78/Overview.html#link">grounded
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HTML link relationships</a>, <a
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href="http://www.w3.org/2000/07/hs78/Overview.html#classes1">grounded
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class names</a> as semantic hooks</li>
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</ul>
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<p>see also: initial <a
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href="http://lists.w3.org/Archives/Public/www-rdf-interest/2000Mar/0103.html">21
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Mar screen-scraping message</a></p>
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</li>
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<li>RDF FAQs/ratholes: people vs. their names; what URI to use when the
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RDF syntax doesn't provide one</li>
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</ul>
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<p>see also: <a href="#Introduction">this section of a swell paper</a></p>
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</li>
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<li>Schema/Ontology basics: Classes, properties
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<ul>
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<li>demo: <a href="http://www.w3.org/2000/07/hs78/algernon">algernon
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taxonomy</a>,
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<ul>
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<li>TODO allow global references in the Classes idiom</li>
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<li>NOTE: a technique for splitting property names into namespace
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name, local name parts (Jun 27 2000 <a
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href="http://lists.w3.org/Archives/Public/www-rdf-interest/2000Jun/0077.html">problem
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report</a>)</li>
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</ul>
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</li>
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<li>TODO: transcribe the RDF, RDF schema schemas?</li>
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<li>issue: other utility stuff: cardinality, inverses, ...</li>
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</ul>
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</li>
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<li>propositional calculus: introducing <a
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href="http://www.w3.org/2000/07/hs78/FOPC#implies">implies</a>, <a
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href="http://www.w3.org/2000/07/hs78/FOPC#false">false</a>
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<ul>
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<li>advanced RDF: reification (aka quoting)</li>
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</ul>
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</li>
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<li>predicate calculus: introducing <a
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href="http://www.w3.org/2000/07/hs78/FOPC#forall">forall</a> (and in doing
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so, variables)
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<ul>
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<li>show a shoe-rule (horn clause) converted: <a
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href="http://www.w3.org/2000/04shoe-swell/inference">inference
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rules</a>, <a href="http://www.w3.org/2000/04shoe-swell/">Shoe->RDF
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stuff</a></li>
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<li>demo: <a href="http://www.w3.org/2000/07/hs78/lists">in, append,
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reverse list rules</a></li>
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<li>technique: function symbols (manual unwinding)</li>
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<li>technique: n-ary symbols.. potentially automatable. NOTE
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asymmetry</li>
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<li>reduction of Rule structure to FOPC primitives</li>
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<li>need some mechanism to avoid russel's paradox?</li>
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</ul>
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</li>
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<li>Future work:
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<p></p>
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<ul>
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<li>instrumented provers/inference engines (<a
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href="http://www.ilrt.bris.ac.uk/discovery/rdf-dev/rudolf/js-rdf/">js-prolog</a>,
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algernon, euler),</li>
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<li>1st order proof checker (<a
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href="http://lists.w3.org/Archives/Public/sw99/2000JanMar/0002.html">mccune's</a>)?
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or just skip that and go right to HOL</li>
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<li>thinking about the edinburgh logical framework: modelling forAll as
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elf:lambda and an operator on top</li>
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<li>unstriped RDF syntax? does XSLT eliminate the need?<br />
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syntax exploration: <a
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href="http://www.w3.org/2000/07/rdf.xsd">rdf.xsd</a> rdfs.xsd
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inference.xsd <a
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href="http://www.w3.org/2000/07/hs78/lists.xsd">lists.xsd</a><br />
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after chat w/ralph: limit propertyElts to string content and
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rdf:resource; no nested typedNodes; move skolemization to RDF
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producer's job rather than RDF parser's.</li>
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<li>primitive datatypes (<a
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href="http://lists.w3.org/Archives/Public/www-rdf-interest/2000Feb/0026.html">16
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Feb)</a> (<a
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href="http://lists.w3.org/Archives/Public/www-rdf-interest/2000May/0098.html">swick
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12 May</a>: still pending!)</li>
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<li>dan's use case: the calendar app: show me my schedule for today
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(assuming trusted data sources; dealing with untrusted sources
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requires dsig/higher order pf checking stuff)</li>
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<li>massimo's use case: <a
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href="http://www.w3.org/2000/07/scribe-stuff/">the next
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scribe</a></li>
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<li>lynn's use case: any new papers by any of my students? (<a
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href="http://www.ai.mit.edu/people/las/cv.html">cv</a>)</li>
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<li>integrating digital signature</li>
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<li><a
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href="http://www.isi.edu/in-notes/iana/assignments/media-types/model/">model</a>/rdf-xml
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media type spec (<a
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href="http://www.imc.org/ietf-xml-mime/">xml-mime</a>)</li>
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<li>modelling HTTP: out of date info ... and phone number changes:
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algernon ask:tell is like http GET:POST</li>
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</ul>
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</li>
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</ol>
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<h2>An Introduction to the Resource Description Framework (RDF)</h2>
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<p></p>
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<h2><a name="Introduction" id="Introduction">Introduction</a></h2>
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<p><small><em>taken from <a
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href="http://lists.w3.org/Archives/Team/sw-team/2000Jul/0000.html">Some "What
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is RDF" bits </a>Lynn Stein (Mon, Jul 03 2000)</em></small></p>
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<p>Most knowledge representations share a common structure. Semantic
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networks[<a
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href="http://liinwww.ira.uka.de/cgi-bin/bibshow?e=Bj0siu/vojrvf%7d4952686&r=bibtex">Woods</a>],
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hypertext[<a
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href="http://cbl.leeds.ac.uk/nikos/tmp/hypemedia/subsection2_2_1_2.html#SECTION0021200000000000000">Drakos</a>],
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etc. use a a directed, labelled graph structure where nodes represent objects
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and the arcs that connect them represent assertions <a
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href="#arc-as-obj">*note</a>. In frame-based representations [<a
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href="http://liinwww.ira.uka.de/cgi-bin/bibshow?e=Pt0JNNE%60JW/vojrvf%7d927398&r=bibtex">Minsky</a>],
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slot-relations connect role-fillers to a frame; frames themselves may also be
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interconnected by relations such as inheritance. In logical formalisms[<a
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href="http://liinwww.ira.uka.de/cgi-bin/bibshow?e=Bj0Tqbujbm/Sfbtpojoh/vojrvf%7d3317916&r=bibtex">McCarthy</a>],
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binary relations are easily expressed using this property notation, though
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arbitrary n-ary relations require an additional translation mechanism <a
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href="#n-ary">*note</a>.</p>
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<p>The Resource Description Framework [<a href="#RDF">RDF</a>] is an emerging
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standard for the exchange of knowledge in the form of directed, labelled
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graphs. At its core is this notion of a <strong>statement</strong>, with a
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<strong>subject</strong> and an <strong>object</strong> related by a
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<strong>property</strong>. For example</p>
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<blockquote>
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Dan is the author of the program.</blockquote>
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<p>"Dan" is the source, or the subject, of the statement, "is the author of"
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is the property, and "the program" is the object.</p>
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<p>RDF builds on commodity web technologies: Uniform Resource Identifiers[<a
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href="#URI">URI</a>] for identifier syntax, and Extensible Markup Language[<a
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href="#XML">XML</a>] for structured syntax. Each of the subject, object, or
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property in an RDF statement can be a URI. The core of the XML syntax for RDF
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does little more than distinguish the parts of a statement. So, to persue the
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example above, we might represent that statement as:</p>
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<pre><rdf:RDF
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xmlns:rdf="http://www.w3.org/1999/02/22-rdf-ns#"
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xmlns:dublinCore="http://purl.org/dc/elements/1.0/"><br />
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<rdf:Descript<tt>ion about="#theProgram"></tt>
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<tt> </tt><dublinCore:cr<tt>eator>Dan Connolly</dublinCore:creator></tt>
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<tt> </tt></rdf:D<tt>escription></tt><br />
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</rdf:RDF></pre>
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<p>where <i>dublinCore</i> is the namespace for the Dublin Core metadata @@
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(explain XML namespaces in a sentence or two).</p>
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<p>@@@Dan stopped here.</p>
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<p>If this description now exists in some document, it can be given a URI. @@@
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establish example.</p>
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<p>Then we can say</p>
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<p>subject</p>
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<p>predicate</p>
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<p>object</p>
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<p>The subject and object can be any resource. But the predicate must be a
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property @@@</p>
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<p>Stuff on typing, restrictions (domain, range), class, subclass,
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subproperty.</p>
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<p>Need containers, comments, labels, ...?</p>
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<p>Also pictures throughout (that someone else gets to draw).</p>
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<p>Footnotes</p>
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<ol>
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<li><a name="arc-as-obj" id="arc-as-obj">Note</a> that this does not
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preclude the inclusion of arcs as "objects" connected by other arcs.</li>
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<li><a name="n-ary" id="n-ary">Either</a> of two alternatives techniques can
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be used to express n-ary relations using binary properties: currying or
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reification.</li>
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</ol>
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<h2>References</h2>
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<dl>
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<dt>[Rao & Turoff]</dt>
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<dd>Rao, Usha & <a href="http://eies.njit.edu/~turoff/">Turoff</a>,
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Murray. <cite>Hypertext Functionality: A Theoretical Framework</cite>,
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International Journal of Human-Computer Interaction, 1990.</dd>
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<dt>[<a name="Craw90" id="Craw90">Craw90</a>]</dt>
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<dd>Crawford, J. (1990), <a
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href="ftp://ftp.cs.utexas.edu/pub/qsim/papers/Crawford-PhD-91.ps.Z"><cite>Access-Limited
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Logic: A Language for Knowledge Representation</cite></a>, Doctoral
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dissertation, Department of Computer Sciences, University of Texas at
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Austin, Austin, Texas. UT Artificial Intelligence TR AI90-141, October
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1990. (<a
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href="http://www.cs.utexas.edu/users/qr/algernon.html">Algernon and
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Access-Limited Logic</a>)</dd>
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<dt>[<a name="RDF" id="RDF">RDF</a>]</dt>
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<dd>Lassila, Swick [eds], <a
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href="../../TR/1999/REC-rdf-syntax-19990222"><cite>Resource Description
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Framework (RDF) Model and Syntax Specification</cite></a> (World Wide
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Web Consortium Recommendation, 1999)</dd>
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<dd><tt><small>http://www.w3.org/TR/1999/REC-rdf-syntax-19990222</small></tt></dd>
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<dt>[<a name="URI" id="URI">URI</a>]</dt>
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<dd>August 1998 <a
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href="http://www.ietf.org/rfc/rfc2396.txt"><cite>Uniform Resource
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Identifiers (URI): Generic Syntax</cite></a></dd>
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<dd>(RFC 2396) T. Berners-Lee, R. Fielding, L. Masinter</dd>
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<dt>[<a name="XML" id="XML">XML</a>]</dt>
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<dd>Feb 1998: W3C Recommendation: <a
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href="../../TR/1998/REC-xml-19980210"><cite>Extensible Markup Language
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(XML) 1.0</cite></a></dd>
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</dl>
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<h2>Acknowledgements and @@Fodder</h2>
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<ul>
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<li><a
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href="http://lists.w3.org/Archives/Team/sw-team/2000Jul/0000.html">Some
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"What is RDF" bits</a>Lynn Stein (Mon, Jul 03 2000)</li>
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<li><a href="../../DesignIssues/Toolbox.html">Semantic Web Toolbox</a> Tim
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BL, 1999 (in progress)</li>
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<li><a
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href="http://lists.w3.org/Archives/Team/sw-team/2000Jun/0021.html">notes
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from 'modelling inference rules' discussion</a> Ralph R. Swick (Fri, Jun
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23 2000)</li>
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<li><a href="../01/sw/bibliography.html">bibliography from work on DARPA
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proposal</a></li>
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</ul>
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</body>
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</html>
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