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Re: OWL Lite semantics

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Mon, 9 Dec 2002 18:50:39 +0000
Message-ID: <15860.58879.101091.960752@merlin.horrocks.net>
To: Jeremy Carroll <jjc@hplb.hpl.hp.com>
Cc: Jim Hendler <hendler@cs.umd.edu>, www-webont-wg@w3.org

On December 9, Jeremy Carroll writes:
> > Jeremy's proposal is that OWL Lite be both a syntactic and *semantic*
> > "subset" (I use the expression loosely in this case) of OWL DL.
> Nothing loose there ...
> my proposal views a language as a pair:
> < A set of documents,
>    an entailment relationship over the set >
> Then
> OWL DL is a sublanguage of OWL full
>    in that the set of OWL DL documents is a subset of the set of OWL Full 
> documents
>    the OWL DL entailment relationship is a subset of the OWL Full 
> entailment relationship (specifically the restriction of OWL Full 
> entailment to the set of OWL DL documents).

Yes, so an OWL DL reasoner, when asked about entailment between two
documents will either give the *SAME ANSWER* as an OWL full reasoner,
or will refuse to answer on the grounds that the document is outside
the subset it can handle.

> My OWL Lite is a sublanguage of OWL Full
>    the set of OWL Lite documents is a subset of the set of OWL Full documents
>    the OWL Lite entailment relationship is also a subset of the OWL DL 
> entailment relationship.

You have omitted the crucial fact that, in the case of your OWL Lite
proposal, the entailment relationship is NOT the OWL full entailment
relationship restricted to the set of OWL Lite documents, but is
(probably) a subset of this set (intuitively tempting to believe that
this is the case, but it remains to be proved). Thus, OWL Lite
reasoners and OWL DL/full reasoners would give *DIFFERENT ANSWERS* to
questions about entailment w.r.t. OWL Lite documents.

This is *NOT* simply incompleteness w.r.t. OWL DL/full semantics,
because a Lite reasoner would be entitled to answer NO to a question
about entailment when the correct DL/full answer is YES.


> Jeremy
Received on Monday, 9 December 2002 12:50:31 UTC

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