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Re: OWL Lite semantics

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Mon, 9 Dec 2002 18:40:40 +0000
Message-ID: <15860.58280.456904.96909@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:
> 
> (This responds in part to the points raised by Ian, Pat and Peter).
> 
> I think I would rather pose the proposal as a proposal to bless a 
> particularly style of incomplete reasoning.
> 
> Seen from an OWL Full perspective ...
> OWL DL reasoners must be complete with respect to OWL DL semantics and 
> sound with respect to OWL Full semantics.
> Any non-OWL DL entailments found can be distinguished since either the 
> premises or conclusions are syntactically excluded from OWL DL.
> However, at one level an OWL DL reasoner is an incomplete OWL Full reasoner.
> 
> Similarly, under my proposal an OWL Lite reasoner must be complete with 
> respect to the proposed OWL Lite semantics, and sound with respect to the 
> OWL Full semantics. This seems wholly analogous, and will introduce no new 
> practical problems, since the reality is that not every OWL Lite system 
> will provide complete reasoning with respect to the OWL DL semantics over 
> the OWL Lite subset. By giving developers a lower bar to aim at, we can 
> reasonably expect them to hit it, thus aiding interoperability by giving 
> clear (and achievable) subsets to aim at.

NO, NO, NO! The cases are not in the least analogous, as what you are
suggesting is sanctioning OWL Lite reasoners which are *UNSOUND*
reasoners for OWL DL and OWL full.


> I will respond to the requirement to justify the achievability claim later. 
> (tomorrow or wednesday).
> 
> In my opinion, it is unrealisitic to expect all OWL Lite developers to 
> achieve complete reasoning with repect to the current OWL DL semantics over 
> the current subset. We need to do one of:
> - make the subset smaller
> - bless some form of incompleteness
> - change the OWL DL semantics
> 
> I see my proposal as blessing a form of incompleteness.

That may have been your intention, but what you actually suggested was
blessing unsoundness.

It may be unrealistic to expect all OWL Lite (or all OWL DL) reasoners
to be complete. So what. Let them be incomplete if that is
useful/necessary. I fail to see why this should compel us to adopt one
of the "solutions" you suggest above.

Ian

> 
> A motivation for expressing it in terms of another semantic theory is to 
> ensure some hard and fast criterion rather than my woolly 80% type attempts 
> earlier. I particularly noted John Stanton's opposition to that proposal.
> 
> Jeremy
Received on Monday, 9 December 2002 12:40:33 GMT

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