• To: Murali Mani <mani@C...>
• Subject: Re: XML Schema and ontologies
• From: Jonathan Borden <jonathan@o...>
• Date: Tue, 30 Sep 2003 18:49:59 -0400
• Cc: xml-dev@l...
• In-reply-to: <Pine.SOL.4.33.0309301305100.29279-100000@p...>
• References: <Pine.SOL.4.33.0309301305100.29279-100000@p...>
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Murali Mani wrote:

>I had a question:
>
>What role does XML Schema play in semantic web?
>  
>
>In specific, do you think search engines will use XML Schemas at all?? Or
>are there other applications of semantic web that will use XML schemas??
>  
>
The specific area where RDF and OWL use XML Schemas is for datatypes and 
owl:DatatypeProperty's -- currently only for simple datatypes, but 
hopefully in the future for complex i.e. XML datatypes.

The current problem in integrating XML Schema with RDF/OWL _XML_ 
datatypes is that RDF is entirely based on naming things with URIrefs 
(and hence OWL), whereas XML Schema names things (i.e. schema 
components) with QNames. A reasonable integration requires a coherent 
QName -> URI mapping.

If such a mapping were to exist, there is no reason why RDF literals 
might not be typed by their XML Schema type name (the URIref version 
:-), and hence no reason why a Semantic Web query might not be 
constained by XML Schema types e.g.

<owl:DatatypeProperty rdf:ID="foo">
       <rdfs:range 
rdf:resource="http://example.org/XMLSchema/someXMLtype" />
</owl:DatatypeProperty>

where http://example.org/XMLSchema/someXMLtype identifies a complex type 
in an XML Schema. One might similarly use XPointers to create datatypes 
that match patterns.

In any case there have been discussions of this on the WebOnt WG lists 
e.g. around 
http://lists.w3.org/Archives/Public/www-webont-wg/2002Nov/0037.html .
I've written up some of the issues at: 
http://www.openhealth.org/WOWG/IssueStructuredDatatypes.html
as well as the discussion on www-rdf-comments: (around) 
http://lists.w3.org/Archives/Public/www-rdf-comments/2002OctDec/0073.html

So, I'd say the answer is that there is no great technical impediment to 
better integrating XML Schema (and RELAXNG for that matter) with the 
Semantic Web via RDF datatypes, but unless there is an interest voiced 
(other than mine) in the proper forums, that the (perhaps) relatively 
small amount of work to accomplish this might not get done.

Jonathan

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