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

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Mon, 8 Apr 2002 03:20:10 -0400
Message-Id: <p05101508b8d62843703a@[65.217.30.94]>
To: Ian Horrocks <horrocks@cs.man.ac.uk>
Cc: www-webont-wg@w3.org
>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.

Pat

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Received on Monday, 15 April 2002 10:57:38 GMT

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