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Re: WG: LANG: owl:ontology

From: Jim Hendler <hendler@cs.umd.edu>
Date: Fri, 20 Sep 2002 12:30:51 -0400
Message-Id: <p0511170bb9b0fbaa2590@[10.0.1.2]>
To: "Raphael Volz" <volz@aifb.uni-karlsruhe.de>, "Webont" <www-webont-wg@w3.org>

At 5:28 PM +0200 9/20/02, Raphael Volz wrote:
>hi jeff,
>
>it is actually quite difficult to find something on this issue.
>XInclude itself does not have a problem with namespaces, as the
>complete document is included.
>
>The namespace question arises when XInclude is used in combination
>of XPointer to include a fragment of a document. This fragment is
>specified by the XPointer part of the uri. In our case the XPointer
>must reference all children of the root node (rdf:RDF).
>
>The possibility to state different, equivalent XPointers imposes some
>difficulties for Implementation.
>
>The xpointer spec itself does not talk about the namespace issue either.
>Rather one has to look in the XPath spec, since XPointer relies on XPath
>for the addressing.
>
>Now, the XPath spec provides the answer (although a bit cryptic and with
>clumpsy formulations)
>
>[SECTION 5.4] http://www.w3.org/TR/xpath#namespace-nodes
>
>[...] This means that an element will have a namespace node:
>
>o for every attribute on the element whose name starts with xmlns:;
>o for every attribute on an ancestor element whose name starts xmlns: unless
>the element itself or a nearer ancestor redeclares the prefix;
>o for an xmlns attribute, if the element or some ancestor has an xmlns
>attribute, and the value of the xmlns attribute for the nearest such element
>is non-empty
>
>This means, that all namespaces on the way to the included nodes are
>collected and
>restated at that node. Namespaces with the same prefix that have been
>declared in the
>including ontology (as attributes of rdf:RDF) will be redefined and
>overwritten locally for each node.
>
>Raphael


Having done a little homework on this issue, I'm concerned about any 
sort of Xinclude solution.  Dan and Jeremy can correct me if I'm 
wrong, but looking through documentation on most of the RDF tools I 
use, I don't find support for this feature (and for a number of other 
Xpath and Xquery formulations).  As a result, to process an Owl 
document one would typically have to take it through an XML tool to 
preprocess it, and then through an RDF tool to interpret it (I 
include Owl tools in this).  THis means we would need to get a number 
of new implementations done to make CR.  This would also mean that if 
I wanted to use something from Cyc (or worse DMOZ) and used Xinclude, 
I would be at the "mercy" of the XML vendor with respect to whether 
the whole documents got munged together or not. It is probably the 
case that the RDF tools should handle the XML stuff, and maybe the 
next generation would, but for now I worry that this mechanism would 
limit the acceptance of our tools, in the short term
   Currently, the main mode of using DAML is to parse it using Jena, 
RDFAPI  or other such RDF aware tools and to take the graph or 
Ntriples they create and start the reasoner/tool there.  Thus, 
anything that would add more steps to this process makes me worried, 
even if it is compliant with standards that other people should (but 
often don't) implement.
  -JH

-- 
Professor James Hendler				  hendler@cs.umd.edu
Director, Semantic Web and Agent Technologies	  301-405-2696
Maryland Information and Network Dynamics Lab.	  301-405-6707 (Fax)
Univ of Maryland, College Park, MD 20742	  240-731-3822 (Cell)
http://www.cs.umd.edu/users/hendler
Received on Friday, 20 September 2002 12:31:13 GMT

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