LC Responses/BP2

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To: Bijan Parsia <bparsia@cs.manchester.ac.uk>
CC: public-owl-comments@w3.org
Subject: [LC response] To Bijan Parsia

Dear Bijan,

Thank you for your comment
     <http://lists.w3.org/Archives/Public/public-owl-wg/2009Jan/0106.html>
on the OWL 2 Web Ontology Language last call drafts.

After considering your comment the W3C OWL Working Group has decided that they will restructure the XML Schema as you suggested.

It is important to note that nothing changed with respect to OWL XML ontology documents, that is, an OWL XML ontology document will successfully validate against the new Schema if and only if it successfully validated against the old schema.

Thanks again for making this very useful suggestion. We hope that the changes we have made address your concerns.

Please acknowledge receipt of this email to <mailto:public-owl-comments@w3.org> (replying to this email should suffice). In your acknowledgment please let us know whether or not you are satisfied with the working group's response to your comment.

Regards,
Bijan Parsia
on behalf of the W3C OWL Working Group



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Ok, here's an example of what I *think* but am not *sure* needs

changing.

The current schema makes heavy use of element groups. For example:

<xsd:group name="ClassAxiom">
  <xsd:choice>
    <xsd:element ref="owl:SubClassOf"/>
    <xsd:element ref="owl:EquivalentClasses"/>
    <xsd:element ref="owl:DisjointClasses"/>
    <xsd:element ref="owl:DisjointUnion"/>
  </xsd:choice>
</xsd:group>

Now, suppose you had an ontology and you wanted to retrieve all the ClassAxioms. It seems like you should be able to just query for "ClassAxiom". That information is in the schema!

But because ClassAxiom is a group and not a type, I *believe* that you have to query with the disjunction of the elements instead of just the group name.

I'm not 100% sure of this. What I do know is that you can query in Schema Aware XPath for the supertype in an XML schema and get the subtypes (or the elements matching that supertype). With the current XML Schema, I have not yet managed to get that effect and have some reason to believe that it's impossible.

(One might be able to work around this with functions in XQuery and XSLT, but at quite a bit of cost. My personal first move would be to rewrite the schema and then use that instead of the normative one.)

I further suspect that groups would prevent the automatic generation of nice type hierarchies from the schema using standard techniques.

So, my basic LC comment would be to restructure the XML Schema to be amenable to such techniques (while recognizing the same set of documents). I'd be willing to consider this an editorial change, but I think it'd be hard to argue.

If I'm wrong about groups, then there's no problem :)