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Re: OWL Lite semantics

From: pat hayes <phayes@ai.uwf.edu>
Date: Mon, 9 Dec 2002 18:44:44 -0600
Message-Id: <p05111b36ba1ae8b6ab21@[10.0.100.86]>
To: "Jos De_Roo" <jos.deroo.jd@belgium.agfa.com>
Cc: www-webont-wg@w3.org

>  > > > 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.
>
>Fine, then it should not say NO, but
>   refuse to answer on the grounds
>   that the *entailment relationship*
>   is outside the subset it can handle.
>(to slightly twist your words)
>and that's just incompleteness

Quite. So it might as well just admit that it is incomplete, and then 
we don't need to change the semantics. Considered as a DL it is going 
to be either incomplete or incorrect (considered as a subset of OWL 
Lite). Considered as a simple logic, it will be incomplete 
(considered as a subset of full OWL). Either way, it is going to be 
incomplete. Which is fine.

Pat



>-- ,
>Jos De Roo, AGFA http://www.agfa.com/w3c/jdroo/


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Received on Monday, 9 December 2002 19:45:13 GMT

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