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Re: Proposal and Test cases (Re: skolems: visible differences?)

From: Jeremy Carroll <jjc@hpl.hp.com>
Date: Wed, 16 Jan 2008 15:08:59 +0000
Message-ID: <478E1E0B.6080606@hpl.hp.com>
To: Bijan Parsia <bparsia@cs.man.ac.uk>
CC: OWL Working Group WG <public-owl-wg@w3.org>


following points came up in HP internal discussion:

a) there's currently no conformance requirement to implement entailment 
for OWL systems, and we would not expect such a requirement to be 

Jena implements entailment principally for passsing W3C entailment 
tests, rather than for end user functionality. The Jena implementation 
is fairly similar to the RIF implementation: on the LHS of an entailment 
a bnode is effectively skolemized, on the RHS a bnode becomes a variable 
in a SPARQL query.

b) Bijan's proposal seems problematic for OWL Full, because bnodes 
corresponding to individuals get treated differently from structural 
bnodes (for example those introduced as part of an intersectionOf 
construct, with its rdf:List ...)

c) strong support that Skolemization is a legitimate OWL implementation 
technique, and suggestion that the OWL WG should review the specs 
shortly before last call to ensure that nothing is said that furthers 
the misreading that Skolemization is not permitted. Some text explicit 
permitting Skolemizing implementations may be advisable.


in summary, not in favour of Skolemized semantics; but in favour of 
Skolemizing implementations.

Received on Wednesday, 16 January 2008 15:09:21 UTC

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