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LC Comment on Entailment Regimes: Class and Property Variables take DL regime beyond FOL

From: Michael Schneider <schneid@fzi.de>
Date: Tue, 26 Jul 2011 13:02:24 +0200
Message-ID: <4E2E9EC0.10707@fzi.de>
To: <public-rdf-dawg-comments@w3.org>
Dear all!

Document: SPARQL 1.1 Entailment Regimes
State: LCWD

The first paragraph in Chap. 6 "OWL 2 Direct Semantics Entailment 
Regime" states that variables are allowed in place of class names and 
property names. Nothing is said, however, about what the semantic 
consequences are of such enhanced flexibility.

If one tries to conservatively extend the OWL 2 Direct Semantics [1] to 
support such queries, the only way I see is to do this by a translation 
into quantifying over variables for unary and binary relations (note 
that under the Direct Semantics, classes and properties are sets and 
binary relations, respectively). In other words, such a semantics goes 
beyond first-order logic (FOL). This is significant, as the OWL 2 Direct 
Semantics was designed as a fragment of standard FOL.

I do not suggest to change the current specification, since I consider 
variables in class and property position to be useful. What I suggest is 
to make the "non-FOL issue" explicit in the document, to make 
implementers aware of it. I suggest to put such a discussion in Sec. 
6.4, which is already dedicated to "Higher Order Queries", but does not 
treat this issue.

[1] <http://www.w3.org/TR/2009/REC-owl2-direct-semantics-20091027/>

Best regards,
Michael

-- 
Dipl.-Inform. Michael Schneider
Research Scientist, Information Process Engineering (IPE)
Tel  : +49-721-9654-726
Fax  : +49-721-9654-727
Email: michael.schneider@fzi.de
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Received on Tuesday, 26 July 2011 11:03:05 GMT

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