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LC Comment: Restriction on Solutions for RDF-Based Entailment Regime

From: Michael Schneider <schneid@fzi.de>
Date: Sat, 30 Jul 2011 19:36:21 +0200
Message-ID: <4E344115.3090504@fzi.de>
To: <public-rdf-dawg-comments@w3.org>
Dear all!

The SPARQL 1.1 Entailment Regimes LCWD, Section 5.2 "Restriction on 
Solutions" in the Chapter defining the OWL 2 RDF-Based Entailment 
Regime, contains an example query consisting of several complex class 
expressions and an Editorial Note, which states

     It could be the case that this example only applies to the
     OWL 2 Direct Semantics and that for the RDF-Based Semantics
     one would have to introduce axioms that force a domain
     element to exist for each extension of the class expressions
     ...

This is correct.

There is, however, an alternative kind of query, which would be close in 
the spirit of the current query, but without suffering from the problem 
of the RDF-Based Semantics that one needs the existence of individuals 
representing class or property extensions:
One can use a query based on a /negative data property assertions/, for 
example in the following form:

     SELECT ?x WHERE {
         _:z rdf:type owl:NegativePropertyAssertion ;
         _:z owl:sourceIndividual ex:peter ;
         _:z owl:assertionProperty ex:dp ;
         _:z owl:targetValue ?x .
     }

The expected possible results of this query would, as for the current 
query, be all literals L to which ex:peter does /not/ have a 
ex:dp-relationship, e.g. L := "6"^^xsd:integer and so on, so the result 
set would be infinite, if not restricted.

There is a specific RDF-based semantic condition that ensures the 
existence of such a "_:z" that combines the triples in the multi-triple 
representation of negative property assertions:

 
<http://www.w3.org/TR/2009/REC-owl2-rdf-based-semantics-20091027/#item-semcond-negassert-data-bw>

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
WWW  : http://www.fzi.de/michael.schneider
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Received on Saturday, 30 July 2011 17:36:51 GMT

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