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321 lines
12 KiB
321 lines
12 KiB
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
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"http://www.w3.org/TR/REC-html40/loose.dtd">
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<html>
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<!-- $Revision: 1.8 $ $Date: 1999/10/08 18:21:06 $ -->
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<title>The Cambridge Communiqué</title>
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<link rel="stylesheet" type="text/css"
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href="http://www.w3.org/StyleSheets/TR/W3C-NOTE">
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<link rel="meta" type="text/xml"
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href="http://www.w3.org/1999/.status/schema-arch/metadata.rdf">
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</head>
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<body>
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<div class="head">
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<a href="http://www.w3.org/"><img alt="W3C" width="72" height="48" border="0"
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src="http://www.w3.org/Icons/WWW/w3c_home" /></a>
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<h1>
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The Cambridge Communiqué
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</h1>
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<h2>
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W3C NOTE 7 October 1999
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</h2>
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<dl>
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<dt>This version:</dt>
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<dd><a href="http://www.w3.org/TR/1999/NOTE-schema-arch-19991007">http://www.w3.org/TR/1999/NOTE-schema-arch-19991007</a></dd>
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<dt>Latest version:</dt>
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<dd><a href="http://www.w3.org/TR/schema-arch">http://www.w3.org/TR/schema-arch</a></dd>
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<dt>Previous version:</dt>
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<dd><a href="http://www.w3.org/1999/08/27-communique-19990920">http://www.w3.org/1999/08/27-communique-19990920</a></dd>
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<dt>Editors:</dt>
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<dd><a href="http://www.w3.org/People/">Ralph R. Swick</a>
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<<a href="mailto:swick@w3.org">swick@w3.org</a>><br />
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<a href="http://www.ltg.ed.ac.uk/~ht/">Henry S. Thompson</a>,
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<<a href="mailto:ht@cogsci.ed.ac.uk">ht@cogsci.ed.ac.uk</a>></dd>
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</dl>
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<p class="copyright">
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<a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"><br />
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Copyright</a> © 1999 <a href="http://www.w3.org/">W3C</a><sup>®</sup>
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(<a href="http://www.lcs.mit.edu/">MIT</a>,
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<a href="http://www.inria.fr/">INRIA</a>,
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<a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C
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<a href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
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<a href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>,
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<a href="http://www.w3.org/Consortium/Legal/copyright-documents">document
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use</a> and
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<a href="http://www.w3.org/Consortium/Legal/copyright-software">software
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licensing</a> rules apply.
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</p>
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<hr title="Separator for header" />
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</div>
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<h2><a name="abstract">Abstract</a></h2>
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<p>
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This document is a report of the results of a meeting of a group of W3C
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Members involved in <a href="http://www.w3.org/XML">XML</a> and
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<a href="http://www.w3.org/RDF">RDF</a> to advance the general
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understanding of a unified approach to the expression of Web data models.
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This document is one response to the Web data architecture discussed
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in "<a href="http://www.w3.org/1999/06/07-WebData">Web Architecture:
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Describing and Exchanging Data</a>".
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</p>
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<h2><a name="status">Status of this document</a></h2>
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<p>
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This document is a W3C Note made available by the World Wide Web Consortium.
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Public comments may be directed to the
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<a href="mailto:www-rdf-comments@w3.org">RDF comments list</a>
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(<a href="http://lists.w3.org/Archives/Public/www-rdf-comments/">archive</a>)
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or to the
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<a href="mailto:www-xml-schema-comments@w3.org">XML Schema comments list</a>
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(<a href="http://lists.w3.org/Archives/Public/www-xml-schema-comments/">archive</a>).
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</p>
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<p>
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Publication of a W3C Note does not imply endorsement by the entire W3C
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Membership. A list of current W3C technical reports and publications,
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including Working Drafts and Notes, can be found at <a
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href="http://www.w3.org/TR">http://www.w3.org/TR</a>.
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</p>
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<p><em>
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This section represents the status of this document at the time this
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version was published. It will become outdated if and when a new
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version is published. The latest
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<a href="http://www.w3.org/1999/.status/schema-arch/status">status</a>
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is maintained at the W3C.</em>
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</p>
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<h2>Contents</h2>
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<ol>
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<li><a href="#introduction">Introduction</a></li>
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<li><a href="#background">Background</a></li>
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<li><a href="#observations">Observations and Recommendations</a></li>
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<li><a href="#conclusions">Conclusions</a></li>
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<li><a href="#signatories">Signatories</a></li>
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</ol>
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<hr />
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<a name="introduction"></a>
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<h2>
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1. Introduction
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</h2>
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<p align="justify">
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A group consisting of W3C Member representatives and W3C staff
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involved in the
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<a href="http://www.w3.org/XML/">XML</a> and
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<a href="http://www.w3.org/RDF/">RDF</a> activities
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<a href="http://www.w3.org/1999/06/schema-core-meeting">met</a>
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[<a href="/Help/AccessForm">members only</a>]
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on August 26 and 27 to discuss the architectural
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relationship between the schema work being undertaken within these two
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activities. The goals of this meeting were to articulate a vision of
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this relationship for the Web community, to feed input into the
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XML Schema
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<a href="http://www.w3.org/XML/Activity#schema-wg">Working Group</a>
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and other W3C activities in support of this
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vision, and to resolve issues raised in the Member review of the
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<a href="http://www.w3.org/TR/1999/PR-rdf-schema-19990303">RDF Schema
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Proposed Recommendation</a> concerning overlap with XML work.
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</p>
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<a name="background"></a>
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<h2>
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2. Background
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</h2>
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<p align="justify">
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The group discussed a wide range of relevant issues which have in
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common the goal of supporting the exchange of data on the Web:
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</p>
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<ol>
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<li>
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<a href="http://www.w3.org/TR/1998/REC-xml-19980210">XML</a>
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has defined a transfer syntax for tree-structured documents;</li>
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<li>
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Many data-oriented applications are being defined which build
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their own data structures on
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top of an XML document layer, effectively using XML documents as a
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transfer mechanism for structured data;</li>
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<li>
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<a href="http://www.w3.org/TR/1999/REC-rdf-syntax-19990222">RDF</a>
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is a W3C recommendation which already employs this layered
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approach. RDF is a member of the Entity-Relationship modelling
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family in which data structured as directed labelled graphs
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can be exchanged via XML documents using a specific XML grammar;</li>
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<li>
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It is a goal to facilitate the use of RDF mechanisms to access
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the information contained in a broad range of XML documents,
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including those that were not initially structured according
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to the RDF 1.0 layering.</li>
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</ol>
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<p align="justify">
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As the expressive facilities available in the XML family, which
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includes RDF, become richer we need an understanding of how these
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facilities relate to similar mechanisms available within other
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formalisms that have adopted XML as their transfer syntax.
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</p>
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<a name="observations"></a>
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<h2>
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3. Observations and Recommendations
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</h2>
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<p align="justify">
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This group reached consensus on the following observations and recommendations:
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</p>
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<ol>
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<li>
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The XML data model is the
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<a href="http://www.w3.org/TR/xml-infoset">XML Information Set</a>
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being specified by the XML Information Set
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<a href="http://www.w3.org/XML/Activity#core-wg">Working Group</a>.
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Other data models exist, both
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generic and application-specific.
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RDF is an example of one such generic data model.
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The XML Schema and RDF Schema
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languages are separate languages based on different data
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models and do not need to be merged into a single comprehensive
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language.</li>
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<li>
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An XML Schema schema document will be able to hold declarations for
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validating instance documents.
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It should also be able to hold declarations for mapping from instance
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document XML infosets to application-oriented data structures.</li>
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<li>
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For evolvability and interoperability, the
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XML Schema specification should provide an extension mechanism
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allowing for
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the augmentation of XML Schema schemas with additional material.
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At a minimum, XML Schema should permit elements from other
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namespaces to be included in schema documents. This extension mechanism
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should also permit individual extensions to be marked 'mandatory',
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meaning that a document instance cannot be deemed 'schema valid'
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if the processing required by a marked extension cannot be performed.</li>
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<li>
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The extension mechanism should be appropriate for use to incorporate
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declarations ("mapping declarations") to aid the construction
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of application-oriented data structures (e.g. ones implementing
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the RDF model) as part of the schema-validation and XML infoset
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construction process. This facility should not be exclusive to
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RDF, but should also be useable to guide the construction of data
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structures conforming to other data models, e.g.
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<a href="http://www.omg.org/techprocess/meetings/schedule/Technology_Adoptions.html#tbl_UML_Specification">UML</a>.</li>
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<li>
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Such mapping declarations should ideally also be useable by other
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schema processors to map in the other direction, i.e. from
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application-oriented data structures to XML infosets.</li>
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<li>
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Many schema languages and query languages are or could be layered on top
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of the XML foundation. RDF Schema is one such language. It is
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appropriate that some mechanisms will apply to both layers and some will
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only apply to one or the other.</li>
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<li>
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XML Schema does not need to be the sole provider of support for
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layering application data structures on XML.
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<a href="http://www.w3.org/TR/xslt">XSLT</a>, with a
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proposed extension mechanism,
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could be used for specifying mappings from XML document
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instances to application data structures - including RDF graphs.
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The reversibility of mappings specified with XSLT or similar
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transformation languages is an issue.</li>
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<li>
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A new simplified XML transfer syntax for RDF and an API for
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accessing RDF data models should be produced. The
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<a href="http://www.w3.org/TR/REC-rdf-syntax/#grammar">RDF 1.0 transfer
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syntax</a> remains a W3C Recommendation and applications are free to
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continue to use it. It is not a requirement that XML Schema be able
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to validate conformance to the full grammar of RDF 1.0 syntax
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(e.g. equivalence of elements and attributes).</li>
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<li>
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XML Schema type hierarchies and RDF type hierarchies are not the same
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and need not be unified; in particular, it is too soon to tell if
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RDF schemas can leverage XML Schema archetypes. However the atomic
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data types, notably URIref, should be shared and work needs to be
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done to support this.</li>
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</ol>
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<a name="conclusions"></a>
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<h2>
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4. Conclusions
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</h2>
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<p align="justify">
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The attendees understand that the XML Schema Working Group is presently
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addressing some of these topics in the context of its existing
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<a href="http://www.w3.org/TR/NOTE-xml-schema-req">Requirements Document</a>.
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We trust that the consensus developed at this
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meeting will help the XML Schema Working Group prioritize features for XML
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Schema 1.0 and will also help the W3C Director while considering the next
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steps for RDF Schema.
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</p>
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<a name="signatories"></a>
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<h2>
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5. Signatories
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</h2>
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<p>
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David Beech, <em>Oracle Corp.</em><br />
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Gabe Beged-Dov, <em>Rogue Wave Software</em><br />
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Tim Berners-Lee, <em>W3C</em><br />
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Dan Brickley, <em>University of Bristol</em><br />
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Allen Brown, <em>Microsoft</em><br />
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Peter Chen, <em>Bootstrap Alliance</em><br />
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David Cleary, <em>Progress Software</em><br />
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Ron Daniel, <em>DATAFUSION</em><br />
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Andrew Eisenberg, <em>Progress Software</em><br />
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David Epstein, <em>IBM</em><br />
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George Feinberg, <em>Object Design</em><br />
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R.V. Guha (<em>unable to attend but endorsing this communiqué</em>)<br />
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Ora Lassila, <em>Nokia</em><br />
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Eve Maler, <em>ArborText, Inc.</em><br />
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Ashok Malhotra, <em>IBM</em><br />
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Murray Maloney, <em>Commerce One</em><br />
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Noah Mendelsohn, <em>Lotus</em><br />
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Eric Miller, <em>OCLC</em><br />
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Wei Song, <em>SISU</em><br />
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Ralph Swick, <em>W3C</em><br />
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Henry Thompson, <em>University of Edinburgh</em>
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</p>
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<p></p>
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<address><small>
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$Date: 1999/10/08 18:21:06 $<br />
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<a href="http://www.w3.org/People/">Ralph R. Swick</a>
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<<a href="mailto:swick@w3.org">swick@w3.org</a>>
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and
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<a href="http://www.ltg.ed.ac.uk/~ht/">Henry S. Thompson</a>,
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<<a href="mailto:ht@cogsci.ed.ac.uk">ht@cogsci.ed.ac.uk</a>>,
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rapporteurs
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</small>
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</address>
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<p>
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<small>
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Revision History:
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<br />1999-09-13T19:54 published
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<br />1999-09-13T20:35 correct Daniel affiliation
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<br />1999-09-15T14:34 add a signature
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<br />1999-09-15T14:40 add document id to the document itself
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<br />1999-09-20T13:19 update Status to direct comments to public archives
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<br />1999-10-07T17:25 add abstract, table of contents, update status
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</small>
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</p>
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</body>
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</html>
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