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

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Thu, 25 Apr 2002 08:59:23 +0100 (BST)
Message-ID: <15559.46939.513550.917953@excalibur.oaklands.net>
To: Pat Hayes <phayes@ai.uwf.edu>
Cc: www-webont-wg@w3.org
On April 8, Pat Hayes writes:
> >On March 21, Dan Connolly 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.
> >
> >Dan,
> >
> >It seems that, on the basis of a few toy examples where using ad-hoc
> >reasoning seems give the results you want/expect, you conclude that
> >this will be appropriate/adequate for all applications.  I don't find
> >this argument very convincing.
> >
> >Even w.r.t. ontology level reasoning I expect things to rapidly get
> >large and complex enough that humans wont be able to check all
> >inferences - we will just have to trust that the reasoner got it
> >right. Soundness is therefore essential,
> 
> True, but
> 
> >and completeness highly
> >desirable.
> 
> That is much less clear. Can you spell out the actual argument for 
> completeness here? I have argued very strongly in the past for 
> completeness, but that was in a different context: Krep in AI, where 
> completeness provides a methodological security against 
> overconfidence in thinking that ones representation captures more 
> content than it really does capture. I don't see that issue as being 
> at all central in applied ontology work, particularly on the web.
> 
> >For example, when multiple processes are interacting, some
> >action may be taken by one process on the basis of a non-inference by
> >another process
> 
> That is a nonmonotonic process, which can lead to unsoundness even 
> with a complete reasoner. So this seems irrelevant.
> 
> >, so incompleteness can easily lead to "unsoundness".
> >
> >As far as the disjointness of object/data domains and properties is
> >concerned, there are also good pragmatic reasons for this, including
> >the ability to use hybrid designs for OWL reasoners, i.e., the ability
> >for an owl "object class" reasoner implementation to "bolt on" a type
> >checker for arbitrary type systems.
> 
> But such reasoners could still be USED: the use of the more liberal 
> syntax does not make such reasoners illegal, only possibly less 
> universally effective. The real issue is whether the web content 
> language needs to be protected against the risk that it might be able 
> to express something that many reasoners could not fully utilize. I 
> would suggest that as a very basic web-methodological point, we 
> should NOT take such worries as being central concerns in the design 
> of OWL. The whole web context means that we cannot forsee the kinds 
> of inference engine that are going to be used, and we should not let 
> the content language be limited by the needs of the engines that we 
> happen to know and love at present. It may well be the case that 
> particular areas of usage will discover, and utilize, combinations of 
> features which allow for pragmatically useful reasoners that work in 
> syntactic subclasses that cut across our current implementation 
> experience.

To reiterate, my suggestion is only that we design the language in
such a way that it is possible to design/implement effective decision
procedures. Of course the definition of "effective" could/will be
contentions. Allowing mixed domains will certainly make life more
difficult for most system implementors as their reasoners may need a
fairly detailed understanding of the characteristics of the domain in
question.

For example, it would be quite easy to assert that every element of
the domain of discourse is a value in some datatype. In this case a
reasoner may have to consider interactions between the cardinality of
the datatype and models of the abstract domain.

Ian

> 
> Pat
> 
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Received on Thursday, 25 April 2002 10:36:57 GMT

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