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<h1>
The Cambridge Communiqu&eacute;
</h1>

<h2>
W3C NOTE 7 October 1999
</h2>

<dl>
 <dt>This version:</dt>
 <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>

 <dt>Latest version:</dt>
 <dd><a href="http://www.w3.org/TR/schema-arch">http://www.w3.org/TR/schema-arch</a></dd>

 <dt>Previous version:</dt>
 <dd><a href="http://www.w3.org/1999/08/27-communique-19990920">http://www.w3.org/1999/08/27-communique-19990920</a></dd>

 <dt>Editors:</dt>
 <dd><a href="http://www.w3.org/People/">Ralph R. Swick</a>
     &lt;<a href="mailto:swick@w3.org">swick@w3.org</a>&gt;<br />
     <a href="http://www.ltg.ed.ac.uk/~ht/">Henry S. Thompson</a>,
     &lt;<a href="mailto:ht@cogsci.ed.ac.uk">ht@cogsci.ed.ac.uk</a>&gt;</dd>
</dl>

<p class="copyright">
  <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"><br />
  Copyright</a> &copy; 1999 <a href="http://www.w3.org/">W3C</a><sup>&reg;</sup>
  (<a href="http://www.lcs.mit.edu/">MIT</a>,
  <a href="http://www.inria.fr/">INRIA</a>,
  <a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C
  <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
  <a href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>,
  <a href="http://www.w3.org/Consortium/Legal/copyright-documents">document
  use</a> and
  <a href="http://www.w3.org/Consortium/Legal/copyright-software">software
  licensing</a> rules apply.
</p>

<hr title="Separator for header" />
</div>

<h2><a name="abstract">Abstract</a></h2>

<p>
This document is a report of the results of a meeting of a group of W3C
Members involved in <a href="http://www.w3.org/XML">XML</a> and
<a href="http://www.w3.org/RDF">RDF</a> to advance the general
understanding of a unified approach to the expression of Web data models.
This document is one response to the Web data architecture discussed
in "<a href="http://www.w3.org/1999/06/07-WebData">Web Architecture:
Describing and Exchanging Data</a>".
</p>

<h2><a name="status">Status of this document</a></h2>

<p>
This document is a W3C Note made available by the World Wide Web Consortium.
Public comments may be directed to the
<a href="mailto:www-rdf-comments@w3.org">RDF comments list</a>
(<a href="http://lists.w3.org/Archives/Public/www-rdf-comments/">archive</a>)
or to the
<a href="mailto:www-xml-schema-comments@w3.org">XML Schema comments list</a>
(<a href="http://lists.w3.org/Archives/Public/www-xml-schema-comments/">archive</a>).
</p>

<p>
Publication of a W3C Note does not imply endorsement by the entire W3C
Membership.  A list of current W3C technical reports and publications,
including Working Drafts and Notes, can be found at <a
href="http://www.w3.org/TR">http://www.w3.org/TR</a>.
</p>

<p><em>
This section represents the status of this document at the time this
version was published. It will become outdated if and when a new
version is published. The latest
<a href="http://www.w3.org/1999/.status/schema-arch/status">status</a>
is maintained at the W3C.</em>
</p>

<h2>Contents</h2>

<ol>
 <li><a href="#introduction">Introduction</a></li>
 <li><a href="#background">Background</a></li>
 <li><a href="#observations">Observations and Recommendations</a></li>
 <li><a href="#conclusions">Conclusions</a></li>
 <li><a href="#signatories">Signatories</a></li>
</ol>

<hr />

<a name="introduction"></a>
<h2>
1.  Introduction
</h2>

<p align="justify">
A group consisting of W3C Member representatives and W3C staff
involved in the
<a href="http://www.w3.org/XML/">XML</a> and
<a href="http://www.w3.org/RDF/">RDF</a> activities
<a href="http://www.w3.org/1999/06/schema-core-meeting">met</a>
[<a href="/Help/AccessForm">members only</a>]
on August 26 and 27 to discuss the architectural
relationship between the schema work being undertaken within these two
activities.  The goals of this meeting were to articulate a vision of
this relationship for the Web community, to feed input into the
XML Schema
<a href="http://www.w3.org/XML/Activity#schema-wg">Working Group</a>
and other W3C activities in support of this
vision, and to resolve issues raised in the Member review of the
<a href="http://www.w3.org/TR/1999/PR-rdf-schema-19990303">RDF Schema
Proposed Recommendation</a> concerning overlap with XML work.
</p>

<a name="background"></a>
<h2>
2.  Background
</h2>

<p align="justify">
The group discussed a wide range of relevant issues which have in
common the goal of supporting the exchange of data on the Web:
</p>
<ol>
<li>
     <a href="http://www.w3.org/TR/1998/REC-xml-19980210">XML</a>
     has defined a transfer syntax for tree-structured documents;</li>
<li>
Many data-oriented applications are being defined which build
     their own data structures on
     top of an XML document layer, effectively using XML documents as a
     transfer mechanism for structured data;</li>
<li>
     <a href="http://www.w3.org/TR/1999/REC-rdf-syntax-19990222">RDF</a>
     is a W3C recommendation which already employs this layered
     approach.  RDF is a member of the Entity-Relationship modelling
     family in which data structured as directed labelled graphs
     can be exchanged via XML documents using a specific XML grammar;</li>
<li>
   It is a goal to facilitate the use of RDF mechanisms to access
   the information contained in a broad range of XML documents,
   including those that were not initially structured according
   to the RDF 1.0 layering.</li>
</ol>
<p align="justify">
As the expressive facilities available in the XML family, which
includes RDF, become richer we need an understanding of how these
facilities relate to similar mechanisms available within other
formalisms that have adopted XML as their transfer syntax.
</p>

<a name="observations"></a>
<h2>
3.  Observations and Recommendations
</h2>

<p align="justify">
This group reached consensus on the following observations and recommendations:
</p>
<ol>
<li>
     The XML data model is the
     <a href="http://www.w3.org/TR/xml-infoset">XML Information Set</a>
     being specified by the XML Information Set
     <a href="http://www.w3.org/XML/Activity#core-wg">Working Group</a>.
     Other data models exist, both
     generic and application-specific.
     RDF is an example of one such generic data model.
     The XML Schema and RDF Schema
     languages are separate languages based on different data
     models and do not need to be merged into a single comprehensive
     language.</li>
<li>
An XML Schema schema document will be able to hold declarations for
     validating instance documents.
     It should also be able to hold declarations for mapping from instance
     document XML infosets to application-oriented data structures.</li>
<li>
For evolvability and interoperability, the
     XML Schema specification should provide an extension mechanism
     allowing for
     the augmentation of XML Schema schemas with additional material.
     At a minimum, XML Schema should permit elements from other
     namespaces to be included in schema documents.  This extension mechanism
     should also permit individual extensions to be marked 'mandatory',
     meaning that a document instance cannot be deemed 'schema valid'
     if the processing required by a marked extension cannot be performed.</li>
<li>
The extension mechanism should be appropriate for use to incorporate
     declarations ("mapping declarations") to aid the construction
     of application-oriented data structures (e.g. ones implementing
     the RDF model) as part of the schema-validation and XML infoset
     construction process.  This facility should not be exclusive to
     RDF, but should also be useable to guide the construction of data
     structures conforming to other data models, e.g.
     <a href="http://www.omg.org/techprocess/meetings/schedule/Technology_Adoptions.html#tbl_UML_Specification">UML</a>.</li>
<li>
Such mapping declarations should ideally also be useable by other
     schema processors to map in the other direction, i.e. from
     application-oriented data structures to XML infosets.</li>
<li>
Many schema languages and query languages are or could be layered on top
of the XML foundation.  RDF Schema is one such language.  It is
appropriate that some mechanisms will apply to both layers and some will
only apply to one or the other.</li>
<li>
XML Schema does not need to be the sole provider of support for
     layering application data structures on XML.
     <a href="http://www.w3.org/TR/xslt">XSLT</a>, with a
     proposed extension mechanism,
     could be used for specifying mappings from XML document
     instances to application data structures - including RDF graphs.
     The reversibility of mappings specified with XSLT or similar
     transformation languages is an issue.</li>
<li>
A new simplified XML transfer syntax for RDF and an API for
     accessing RDF data models should be produced.  The
     <a href="http://www.w3.org/TR/REC-rdf-syntax/#grammar">RDF 1.0 transfer
     syntax</a> remains a W3C Recommendation and applications are free to
     continue to use it.  It is not a requirement that XML Schema be able
     to validate conformance to the full grammar of RDF 1.0 syntax
     (e.g. equivalence of elements and attributes).</li>
<li>
XML Schema type hierarchies and RDF type hierarchies are not the same
     and need not be unified; in particular, it is too soon to tell if
     RDF schemas can leverage XML Schema archetypes.  However the atomic
     data types, notably URIref, should be shared and work needs to be
     done to support this.</li>
</ol>

<a name="conclusions"></a>
<h2>
4.  Conclusions
</h2>

<p align="justify">
The attendees understand that the XML Schema Working Group is presently
addressing some of these topics in the context of its existing
<a href="http://www.w3.org/TR/NOTE-xml-schema-req">Requirements Document</a>.
We trust that the consensus developed at this
meeting will help the XML Schema Working Group prioritize features for XML
Schema 1.0 and will also help the W3C Director while considering the next
steps for RDF Schema.
</p>

<a name="signatories"></a>
<h2>
5.  Signatories
</h2>

<p>
 David Beech, <em>Oracle Corp.</em><br />
 Gabe Beged-Dov, <em>Rogue Wave Software</em><br />
 Tim Berners-Lee, <em>W3C</em><br />
 Dan Brickley, <em>University of Bristol</em><br />
 Allen Brown, <em>Microsoft</em><br />
 Peter Chen, <em>Bootstrap Alliance</em><br />
 David Cleary, <em>Progress Software</em><br />
 Ron Daniel, <em>DATAFUSION</em><br />
 Andrew Eisenberg, <em>Progress Software</em><br />
 David Epstein, <em>IBM</em><br />
 George Feinberg, <em>Object Design</em><br />
 R.V. Guha (<em>unable to attend but endorsing this communiqu&eacute;</em>)<br />
 Ora Lassila, <em>Nokia</em><br />
 Eve Maler, <em>ArborText, Inc.</em><br />
 Ashok Malhotra, <em>IBM</em><br />
 Murray Maloney, <em>Commerce One</em><br />
 Noah Mendelsohn, <em>Lotus</em><br />
 Eric Miller, <em>OCLC</em><br />
 Wei Song, <em>SISU</em><br />
 Ralph Swick, <em>W3C</em><br />
 Henry Thompson, <em>University of Edinburgh</em>
</p>

<p></p>

<address><small>
$Date: 1999/10/08 18:21:06 $<br />
<a href="http://www.w3.org/People/">Ralph R. Swick</a>
&lt;<a href="mailto:swick@w3.org">swick@w3.org</a>&gt;
and
<a href="http://www.ltg.ed.ac.uk/~ht/">Henry S. Thompson</a>,
&lt;<a href="mailto:ht@cogsci.ed.ac.uk">ht@cogsci.ed.ac.uk</a>&gt;,
rapporteurs
</small>
</address>

<p>
<small>
Revision History:
<br />1999-09-13T19:54 published
<br />1999-09-13T20:35 correct Daniel affiliation
<br />1999-09-15T14:34 add a signature
<br />1999-09-15T14:40 add document id to the document itself
<br />1999-09-20T13:19 update Status to direct comments to public archives
<br />1999-10-07T17:25 add abstract, table of contents, update status
</small>
</p>

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