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Re: [OWL-S] Proposal for Making Progress on Process Modeling esp. Preconditons and Effects

From: Michael Kifer <kifer@cs.stonybrook.edu>
Date: Thu, 15 Jan 2004 18:25:34 -0500
To: Bijan Parsia <bparsia@isr.umd.edu>
Cc: public-sws-ig@w3.org, www-rdf-rules@w3.org
Message-Id: <20040115232535.3155619E67F@kiferdesk.kiferhome.com>


Bijan Parsia <bparsia@isr.umd.edu> wrote:
> 
> On Jan 15, 2004, at 12:42 PM, Michael Kifer wrote:
> 
> >> Bijan Parsia <bparsia@isr.umd.edu> wrote:
> [snip]
> >> I'd be interested in a CTL based axiomization of OWL-S. Are you doing
> >> one for SWSL?
> >
> > I am planning to do it this week as part of my SWSL action item.
> 
> Great, looking forward.
> 
> >
> >> What features would SWRL need to support CTL? How easy is it to  
> >> combine
> >> OWL and CTL?
> >
> > These are two orthogonal things.
> 
> Hence the two questions :) Actually, they aren't quite so distinct as  
> SWRL (at least last I checked) is a proper superset of OWL-DL. There  
> are issues with certain extensions of predicate calculus discussed in  
> the Description Logic Programs paper.
> 
> > CTL extends predicate calculus, while OWL
> > (at least, OWL-DL) is a subset of predicate calculus.
> 
> Sure.
> 
> >  Of course, it is
> > a different issue whether one can make a useful combination out of the  
> > two.
> 
> Er...I have to take this to mean that there might be *more* FOL that  
> one would want than either OWL-DL or SWRL. I.e., if the extensions are  
> compatible with all of FOL, then there's no problem adding them to a  
> subset. The question is whether the extended subset is at all  
> interesting. (E.g., is Concurrent Transaction Propositional Logic  
> interesting from a practical SWS point of view.)

The extended subset may be interesting, but you lose the properties that DL
had when considered alone. So, it might not be any more interesting than
some extended superset of DL. (I just don't know--maybe worth looking into.)


> > In my view, the most important thing(s) about DLs are the subsumption
> > algorithms.
> 
> Really? Subsumption is typically reduced to satisfiability. That is,  
> the core reasoning service is satisfiability. This can be used, in the  
> normal refutation manner, to support relatively arbitrary entailments  
> (there are some issues since you don't typically have direct negation  
> of property assertions, but see Ian and Peter's paper on reducing OWL  
> Entailmen to DL satisfiability:  
> http://www.cs.man.ac.uk/~horrocks/Publications/download/2003/ 
> HoPa03b.pdf)

Subsumption and satisfiability are the same (reducible to each other)
in a sufficiently rich DL.


> > It is not clear how and where you are going to use subsumption
> > when it comes to process models (i.e., sequencing, parallel  
> > composition,
> > loops, etc.).

Or how you can use DL when it comes to process models. You can do with DL
only as much as what you can do with DL.


> See above. There are classification algorithms, but they are mostly  
> optimization oriented, that is, trying to avoid as many subsumption  
> tests as possible. But the standard subsumption test is:
> 	To see if C isSubclassOf D
> 	Take the kb, add (C & ~D)
> 	Check the satisfiability of the resultant kb.
> 		If unsatisfiable, then the subsumption holds.
> 		If not, then it doesn't hold.
> 
> There's nothing magical about subsumption.

Who said there is? It is just that for those restricted subsets of the
logic subsumption (or satisfiability, if you insist) is decidable.


> >> I think Benjamin's example (in figure 1) can be handled in OWL-S, with
> >> simpleprocesses, though perhaps not as elegantly.
> >
> > You can (almost) always avoid defaults for any particular example by
> > blowing up specifications and incorporating exceptions directly into  
> > the
> > spec. The problem with this is that this is inelegant, makes it hard to
> > write the specs, and makes the specs non-compositional. New exceptions
> > must be re-incorporated into the specs, etc. The reason why
> > object-oriented programming became so successful is because it offers a
> > way to avoid all this complexity.
> 
> I'll wait until I've given it a shot to see what you think. I'm not  
> clear that I *would* be avoiding non-mon, per se. Notice I said in  
> *OWL-S*, not in OWL -- much of the semantics of OWL-S descriptions is  
> not expressed in OWL.

OK. But then we don't disagree with each other.


	--michael  
Received on Thursday, 15 January 2004 18:25:44 UTC

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