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Re: SEM: semantics for current proposal (why R disjoint V?)

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Tue, 23 Apr 2002 23:23:10 +0100 (BST)
Message-ID: <15557.57038.633294.367258@excalibur.oaklands.net>
To: Pat Hayes <phayes@ai.uwf.edu>
Cc: Dan Connolly <connolly@w3.org>, www-webont-wg@w3.org
On April 8, Pat Hayes writes:
> >On Thu, 2002-03-21 at 14:28, Ian Horrocks wrote:
> >>  On March 21, Libby Miller writes:
> >>  > >
> >>  > > As noted in the design discussions for DAML+OIL, I don't
> >>  > > see sufficient justification for making V disjoint
> >>  > > from R.
> >>  > >
> >>  > > It seems silly not to be able to talk about the intersection
> >>  > > of two sets of strings, or UniqueProperty's whose
> >>  > > range is dates, or whatever.
> >>
> >>  This means that any OWL reasoner has to take on responsibility for
> >>  reasoning about types
> >
> >I gather when you say "OWL reasoner" you mean a complete
> >reasoner.
> >
> >I'm not very interested in such a thing.
> >
> >Regular old horn-clause/datalog reasoners
> >(with some built-in predicates like
> >string:lessThan and such) seem
> >to get me what I need pretty well.
> >
> >So this argument about negation and complete reasoning
> >doesn't persuade me that we should keep R and V disjoint.
> 
> I agree. Most of the actual reasoning with OWL is likely to be done 
> with PERL scripts and other such ad-hoc and highly incomplete pieces 
> of machinery in any case (how could we prevent this, even if we 
> wanted to? We can't rule it illegal to use an incomplete reasoner), 

This may or may not be true, and nobody (or at least not me) is
suggesting it be illegal to use an incomplete reasoner. I am just
arguing that it should be POSSIBLE to write a (reasonably efficient)
reasoner that is sound and complete (and terminating).

As far as the separation of datatype and abstract domains is
concerned, without this we don't fully understand the formal
properties of the language: it may even be undecidable, and life would
certainly be MUCH more difficult for ANY implementor, even one only
interested in soundness.

As far as the separation of datatype and abstract properties is
concerned, this may be less important.

> so these issues seem largely irrelevant; whereas the inconvenience 
> and artificiality of maintaining the restriction is a real barrier to 
> deployment. There is no *semantic* reason for the distinction.

W.r.t. the domains, the interaction between the concept language and
the built in datatype predicates is at best unpleasant and may even
lead to undecidability (no definitive result at present). I also don't
believe that this is "a real barrier to deployment" (can you show me
examples where users really need objects that are both individuals and
data values?). I believe that a much bigger barrier to deployment
would be devising a language where complete (and perhaps even sound)
reasoners were difficult or impossible to build.

Ian


> 
> Pat Hayes
> 
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Received on Tuesday, 23 April 2002 18:35:18 GMT

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