LC Responses/IH3

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Alan is concerned about citation of our meeting minutes. See message


To: Ivan Herman<ivan@w3.org>
CC: public-owl-comments@w3.org
Subject: [LC response] To Ivan Herman

Dear Ivan,

Thank you for your comment
     <http://lists.w3.org/Archives/Public/public-owl-wg/2009Feb/0007.html>
on the OWL 2 Web Ontology Language last call drafts.

Your comment is closely related to the one by Maurizio (see http://lists.w3.org/Archives/Public/public-owl-comments/2009Jan/0014.html) and Misha (see http://lists.w3.org/Archives/Public/public-owl-comments/2009Jan/0019.html).

The working group has decided to implement the editorial changes and will correct the typos, thanks for pointing them out. We have also decided to add, to OWL 2 QL, reflexive, irreflexive, & asymmetric property axioms.

Finally, we have decided *not* to add sameAs or functional properties to OWL 2 QL:

- [sameAs] OWL 2 QL was designed so that any query Q against an ontology whose data (i.e., information about individuals, the classes they are instances of and how they are related via properties) is stored in a relational database DB, can be answered by rewriting the query Q into an SQL query Q1 and then answering Q1 against DB using a standard RDBMs. This property is known to be lost in the presence of sameAs. For the LOD community, we will add a small paragraph explaining that, if one wants to handle ontologies that are OWL 2 QL plus sameAs, then one can use a preprocessing step that materializes the sameAs relation and uses it in query answering procedures to simulate individual equality reasoning (see http://www.w3.org/2007/OWL/wiki/Profiles#Feature_Overview_2).

- functional properties can only be added under the so-called unique name assumption, i.e., different names denote different indiviudals. This assumption, together with functional properties, will lead to inconsistencies if an individual has 2 successors w.r.t. a functional property -- a semantics that is suitable for some applications and unsuitable for others. Hence we have chosen to not include functional properties to OWL 2QL.

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,
Uli Sattler
on behalf of the W3C OWL Working Group



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From http://lists.w3.org/Archives/Public/public-owl-wg/2009Feb/0007.html

In the current version of OWL QL, owl:sameAs (if you prefer, same individual assertion:-) is disallowed. Having checked with Boris (and also chatted with Bijan) it seems that the reason is that this leaves it open to possibly extend QL *either* to include owl:sameAs *or* (exclusive 'or') functional properties.

In my view, it would be better to include one or the other to the document to make the QL standard profile clearer and cleaner for users. Introducing a loophole of extra extension would reduce the usability of QL in my view, mainly in terms of interoperability.

The LOD movement, for better or worse, has already made an extensive use of owl:sameAs in linking billions of triples stemming from public databases. In view of that use case, my proposal is to _add_ the same individual assertion into OWL QL. That would make OWL QL way more attractive for an important user community.