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Re: Issue: Add hasValue to OWL Lite

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Thu, 31 Oct 2002 15:45:46 +0000
Message-ID: <15809.20522.333312.342014@merlin.horrocks.net>
To: Dan Connolly <connolly@w3.org>
Cc: Deborah McGuinness <dlm@ksl.stanford.edu>, webont <www-webont-wg@w3.org>

On October 29, Dan Connolly writes:
> 
> On Tue, 2002-10-29 at 18:34, Ian Horrocks wrote:
> > 
> > The problem with adding hasValue to OWL Lite is that it wouldn't be
> > Lite any more. The lack of hasValue in Lite is, from an implementation
> > point of view, the main thing that differentiates it from fast -
> > hasValue is very tough to deal with, and is responsible for pushing
> > the worst case complexity of reasoning in fast OWL from ExpTime to
> > NExpTime.
> 
> Could you unpack that a bit?
> 
> Could you give an example, maybe?

I'm not sure. This isn't anything to do with reasoning techniques or
specific examples, it is a fundamental property of the logic that
basic inference problems (satisfiability, subsumption, entailment) are
much harder when we add extensionally defined classes (which is what
hasValue amounts to).

If you want an intuition, it comes down to the loss of the tree(ish)
model property. Without this property, it is very hard to devise
decision procedures that work in a goal-directed way and that know
when they are done.

Ian

> 
> The rules for hasValue that occur to me are:
> 
>  holds(rdf:type, X, C) :-
> 	holds(P, X, Y),
> 	holds(owl:onProperty, C, P),
> 	holds(owl:hasValue, C, Y).
> 
> 
> now that's only a partial specification of hasValue;
> it allows you to come to hasValue conclusions, but
> not to exploit hasValue claims in other ways.
> 
> I'm curious what people actually expect to do with hasValue,
> and what makes hasValue difficult to deal with,
> and whether they overlap.
> 
> If what people want to do is to say
> 
> 	People with birthplace America are Americans
> 	Fred birthplace America
> 	=>
> 	Fred is an American
> 
> then that looks only horn-clause-hard.
> 
> But if they want to do something else, I can imagine
> it would get harder.
> 
> > Ian
> > 
> > On October 26, Deborah McGuinness writes:
> > > 
> > > There have been requests to add hasValue to OWL Lite.  This is a
> > > proposal to include hasValue in OWL Lite.
> 
> [...]
>  
> -- 
> Dan Connolly, W3C http://www.w3.org/People/Connolly/
> 
Received on Thursday, 31 October 2002 10:46:03 GMT

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