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Re: LANG: inverse/onOf interaction

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Thu, 13 Jun 2002 16:25:43 +0100 (BST)
Message-ID: <15624.47479.271040.423382@excalibur.oaklands.net>
To: Jeff Heflin <heflin@cse.lehigh.edu>
Cc: WebOnt <www-webont-wg@w3.org>

On June 13, Jeff Heflin writes:
> 
> Ian Horrocks wrote:
> > 
> > I promised to explain in a bit more detail why inverse properties and
> > oneOf interact adversely (at least as far as reasoning support is
> > concerned).
> > 
> > The combination of these features is very powerful, and it is easy to
> > see how they can be used to build ontologies for which reasoning will
> > be very difficult. One example is the use of a so called "spy-point"
> > to limit the maximum size of the domain of discourse. This is done,
> > e.g., as follows:
> > 
> > 1. Add an axiom asserting that every element in the domain of
> > discourse is related to the individual "Spy" via some property, i.e.,
> > add the axiom Thing subClassOf (hasValue P Spy).
> > 
> > 2. Add an axiom asserting that Spy is related to at most n distinct
> > individuals via the inverse of the P property, i.e., Spy type
> > (maxCardinality (inverse P) n).
> 
> 
> Ian, I don't get it. Where is oneOf used in this example? It seems that
> the combination of hasValue, cardinality, and inverse is what leads to
> this case, not inverse and oneOf. Did you leave something out, or am I
> missing something?

Sorry, I should have been clearer. (hasValue P Spy) is really just
syntactic sugar for (hasClass P (oneOf Spy)). Of course this means
that w.r.t. DAML+OIL one would have to eliminate both oneOf and
hasValue in order to reduce the complexity.

Ian

> 
> Jeff
> 
> > It may be counter-intuitive, but the ability to fix the size of the
> > domain of discourse to some arbitrary size makes reasoning much
> > harder.  From a practical point of view, this can be seen in many
> > "strange" additional inferences: e.g., for ANY property R, the class
> > defined by a restriction (minCardinality R n+1) becomes incoherent
> > (because there can only be n distinct objects in the domain of
> > discourse). From a theoretical point of view, the worst case
> > complexity of basic inference tasks (e.g., class consistency) jumps
> > from Exptime (for DAML+OIL without inverse or without oneOf), to
> > NExpTime for full DAML+OIL. If fact, inference is already NExpTime
> > hard for the basic ALC description logic (booleans plus hasClass and
> > toClass) with the addition of inverse and oneOf.
> > 
> > In fact, the problem boils down to the loss of the tree model
> > property. The language without oneOf has the (transitive) tree model
> > property, that is, any class that has a model has a (transitive) tree
> > model. This means that decision procedures can restrict their
> > attention to this kind of model without sacrificing
> > completeness/corectness. With oneOf but no inverse, things are a bit
> > more complex, but a similar restriced model property can be
> > demonstrated.
> > 
> > You can find some more information, including pointers to various
> > other relevant papers, in [1] (sorry for the self citation).
> > 
> > I hope this helps - no doubt you will let me know if you have any
> > queries.
> > 
> > Ian
> > 
> > [1] http://www.cs.man.ac.uk/~horrocks/Publications/download/2001/ijcai01.pdf
> 
Received on Thursday, 13 June 2002 11:33:11 GMT

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