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Re: CR/PR questions

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Thu, 8 May 2003 18:03:49 +0100
Message-ID: <16058.36341.953696.827807@galahad.cs.man.ac.uk>
To: Jeremy Carroll <jjc@hpl.hp.com>
Cc: www-webont-wg@w3.org

On May 5, Jeremy Carroll writes:
> 
> 
> A short message.
> 
> I am not expecting reasoners to work fast, just to reason successfully within 
> some time period that is less than forever.
> 
> This is not about quantitative capabilities of reasoners, but qualititave 
> capabilities. Can they reason about finite classes and their cardinalities - 
> or are they really only capable of advanced reasoning about infinite classes.
> 
> OWL DL and Full permits descriptions that describe both infinite and finite 
> classes.
> The DL community have much more experience in reasoning about descriptions of 
> infinite classes than finite ones.

Jeremy,

It is hard to understand why this is, in itself, a good reason for
having a lengthy CR period, or what you expect would be achieved
during such a period (unless it were to be years rather than
months). We know that Full is not even decidable.  We know from
DAML+OIL that no effective algorithm for all of DL is available. We
have known for a long time that even our "Lite" language requires, in
the worst case, time exponential in the size of the ontology in order
to perform common reasoning tasks. All of this was accepted by the WG
at the time we were designing the language(s).

As far as your expectation for reasoners to reason "successfully" is
concerned, success may be rather hard to quantify (or even qualify):
the medics here deemed their reasoner to be successful so long as it
was able to classify their ontology overnight - this would obviously be
considered an abject failure in some applications. It is likely that
Lite reasoners will be, in general, more "successful" than DL
reasoners, which will be more "successful" than full reasoners. Your
point about reasoning with finite classes is well made, but a complete
investigation/solution of this problem may take an indefinitely long
time. It might be worth pointing out that DAML+OIL is also able to
express finite classes, and this does not seem to have been a barrier to
its widespread adoption.

Regards, 

Ian



> 
> Jeremy
> 
Received on Thursday, 8 May 2003 12:53:45 GMT

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