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Re: Expressiveness question

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Tue, 27 Jan 2004 20:54:56 +0000
Message-ID: <16406.53280.783694.612407@merlin.horrocks.net>
To: Sheila McIlraith <sheila@cs.toronto.edu>
Cc: pat hayes <phayes@ihmc.us>, www-rdf-rules@w3.org, daml-process@bbn.com

On January 27, Sheila McIlraith writes:
> 
> Ian,
> 
> This is very helpful and interesting.  <Though I need to work through
> an example in more details to understand all of the implications.>
> 
> Regarding the question of whether the disjunctive literals in FOL would be
> encoded as classes or properties in OWL, my sense is that actions (e.g.,
> a=pickup(x)) would be encoded as classes.  I'll think about whether
> fluents in the situation calculus (predicates, indexed by the situation
> term, whose truth value can changes as a result of an action) could be
> encoded as classes as well.

It isn't obvious to me how you can capture the relationship between a
and x using a class, but I will wait to hear more. If it is the case
that you can encode one or other of the disjuncts as classes, then I
believe that you can capture the iff using the rewriting trick that I
described.

Ian

> 
> Sheila
> 
> 
> 
> On Tue, 27 Jan 2004, Ian Horrocks wrote:
> 
> > On January 25, Sheila McIlraith writes:
> > >
> > >
> > > Hi Pat,
> > >
> > >
> > > On Tue, 20 Jan 2004, pat hayes wrote:
> > >
> >
> > [...]
> >
> > > > holding(x, do(a,s)) IMPLIES ((a=pickup(x)) OR (holding(x,s) )
> > > >
> > > > isn't, and isn't ever likely to be stateable in any rule language.
> >
> > But given that in SWRL combines rules with OWL, we get something much
> > more powerful which may allow us to state more that in normal rule
> > languages. E.g., if the disjunction in the head of the rule included a
> > unary predicate:
> >
> > Body IMPLIES P1(x) OR P2(x)
> >
> > then we would be able to state it in SWRL because we can rewrite it as
> >
> > Body AND NOT P2(x) IMPLIES P1(x)
> >
> > SWRL allows us to use (NOT P2) as a predicate (or we could use OWL to
> > assert that the class NOT-P2 as equivalent to the negation of the
> > class P2).
> >
> > Whether or not this kind of trick would work for the rule Pat wrote
> > would depend on how (a=pickup(x)) and (holding(x,s)) are encoded: if
> > they are encoded as binary predicates (OWL properties), then it seems
> > unlikely that we can express it in SWRL as it would amount to
> > providing property negation, and Uli Sattler has managed to convince
> > me that we (almost certainly) can't express property negation in SWRL.
> >
> > Regards,
> >
> > Ian
> >
Received on Tuesday, 27 January 2004 15:59:09 GMT

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