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Re: LANG: issue 5.1 - Uniform treatment of literal/data values

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Thu, 19 Sep 2002 12:53:14 +0100
Message-ID: <15753.47786.117987.104332@galahad.cs.man.ac.uk>
To: Jim Hendler <hendler@cs.umd.edu>
Cc: www-webont-wg@w3.org

This is *NOT* a proposal, half baked or otherwise. It is just a report
on (possibly) relevant ongoing research (my reluctance to provide such
a report was exactly because I was worried that it might be
interpreted as a proposal). 

I have consistently argued against relying on ongoing research in the
current language. If I had to make a proposal I would say to go with
the status quo (which is well understood) and consider adding features
such as keys in future versions/extensions of the language. The
advantage of the keys approach in this regard is that it would be a
direct extension of the DAML+OIL approach, i.e., it simply provides an
additional means for an ontology to constrain the set of admissible
models.

Ian

On September 18, Jim Hendler writes:
> 
> At 3:26 PM +0100 9/18/02, Ian Horrocks wrote:
> >I promised to say something about the possible use of key constraints
> >in this context, so here it is.
> >
> >Carsten Lutz, Ulrike Sattler, Carlos Areces and myself have been
> >looking into the idea of reasoning w.r.t. a set of "key" axioms. These
> >are axioms of the form "C hasKey k1,...,kn", where C is a class and k1
> >to kn are a list of functional datatype properties (in general these
> >could be functional paths, but this usually leads to undecidability).
> >
> >In its simplest form the class C would be Thing, and there would only
> >be a single functional datatype property in each axiom, e.g., "Thing
> >hasKey k". Adding this axiom would be equivalent to making the
> >datatype property k inverse functional. Referring to Dan's state code
> >example, adding the axiom "Thing hasKey stateCode" would support the
> >desired entailment.
> >
> >The problem of reasoning w.r.t. such axioms is similar to (but worse
> >than) the problem of reasoning with nominals (i.e., classes defined
> >extensionally using the oneOf constructor) - in fact it is easy to see
> >that the expressive power of keys subsumes that of nominals because if
> >keyProp is an key for Thing and ranges over the integers, then
> >restriction classes of the form "onProperty keyProp toValue i", where
> >i is an integer, can be used as nominals. It is, however, still
> >possible to separate reasoning w.r.t. datatypes from reasoning
> >w.r.t. the object domain (using a more sophisticated datatype
> >reasoner) s.t. a hybrid reasoner is sound and complete iff both the
> >object and datatype reasoners are sound and complete.
> >
> >Obviously this work is still at a relatively early stage, so I don't
> >want to suggest that it represents any kind of "compromise solution"
> >to the problem (even if such a compromise were acceptable).
> >
> >Regards, Ian
> >
> >[1] http://lists.w3.org/Archives/Public/www-webont-wg/2002Apr/0261.html
> 
> 
> I think some sort of compromise is needed, here is a half-baked 
> proposal that might be useful in continuing the discussion
> 
> Suppose we continue to have data and object properties distinguished, 
> but with some sort of syntactic construct that would let one do an 
> association that allows keys- as follows:
> 
> :SSnum a owl:dataTypeProperty.
> :Individual a owl:class.
> :Individual a owl:ObjectTypeProperty.
> :SSnum owl:dataDesignatesUniqueObject :Individual.   (needs a better name)
> 
> which would be a syntactically special way to say inverseFunctional 
> on a datatype.  (This would allow keys and some other similar uses). 
> The advantage is that there would be a syntactic flag to know this is 
> occuring so that Fact and other reasoners could say "If you use this 
> property, you may not get completeness" -- in short, this is a 
> variant on Jeremy's "here be dragons" approach -- but since, at least 
> I think, the inverseFunctional on datatypes would mostly be used by 
> people doing things to instances (rather than class reasoning) this 
> wouldn't be a major problem.
>   Dan's states examples seem to be satisfied by this (details left as 
> exercise to reader) and it also allows distinguished data and type 
> classes for tools like RIC that can profit from knowing which is 
> which.
> 
>   -JH
> p.s. Please note this message doesn't say "chair neutrality off" - 
> I'm not putting forth my personal preference here, but trying to get 
> discussion restarted.
> -- 
> Professor James Hendler				  hendler@cs.umd.edu
> Director, Semantic Web and Agent Technologies	  301-405-2696
> Maryland Information and Network Dynamics Lab.	  301-405-6707 (Fax)
> Univ of Maryland, College Park, MD 20742	  240-731-3822 (Cell)
> http://www.cs.umd.edu/users/hendler
> 
Received on Thursday, 19 September 2002 07:46:21 GMT

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