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Re: OWL reasoning in rules - infinite domains and queries

From: Matt Williams <matthew.williams@cancer.org.uk>
Date: Wed, 30 May 2007 19:08:49 +0100
Message-ID: <465DBDB1.3020107@cancer.org.uk>
To: Taowei David Wang <tw7@cs.umd.edu>
CC: Jeremy Carroll <jjc@hpl.hp.com>, Ulrike Sattler <sattler@cs.man.ac.uk>, Ian Horrocks <horrocks@cs.man.ac.uk>, Owl Dev <public-owl-dev@w3.org>, Semantic Web <semantic-web@w3.org>, Bijan Parsia <bparsia@cs.man.ac.uk>

Dear All,

Following on from this discussion, and Ulrike's paper, if we have 
infinite (inferred) individuals, such as chains of fathers or Guards, 
and we query the ontology, what is returned?

Would a query of the form Guard(x) or Father(x) return an infinite 
number of bindings? Or can we restrict it to "Known" individuals (which 
seems to be what Ulrike's paper suggests). Is this similar to what you 
can do with some of the SPARQL implementations (e.g. in Pellet) where 
you can allow/ disallow bNodes - or is this distinct (I suspect they're 
different - the rdf graph is not, I hope, infinite).

Thanks,

Matt



Taowei David Wang wrote:
>> Hmmm, I would like to see a small ontology which is necessarily infinite.
> 
> As the movie 300 has made the Greek phalanx popular again, here is a small
> ontology that contains a class that has only infinite models:
> 
> Guard subclassOf ( (some shields.Guard) and ( <2 inverse(shields)) )
> FirstGuard subclassOf ( Guard and ( <1 inverse(shields) )
> 
> "Every Guard shields some Guard, and is in turn shielded by at most 1
> Guard."
> 
> "A FirstGuard is a Guard, and is not shielded by another."
> 
> FirstGuard has no finite model, because it generates an
> infinite number of Guards (every Guard needs to shield someone, and it
> can't be the FirstGuard).
> 
> The above example is found in this paper (Page 4, Sec 3):
> 
> http://citeseer.ist.psu.edu/calvanese96finite.html
> 
> other refs on topics of computing finite models in DL:
> 
> http://citeseer.ist.psu.edu/710125.html
> http://www.inf.unibz.it/~franconi/dl/course/articles/reasoning-survey.ps.gz
> 
> I am sure others would chime in with newer papers, but these were helpful
> to me.
> 
> Cheers,
> 
> Dave
> ----
> 
> 
>> I've just being looking with google, and found my own
>> http://www.w3.org/TR/owl-test/dl-900-arith#description-logic-908
>>
>> which I believe hinges on
>>     2*3*n = 5*n & n>0
>>      implies n >= aleph0,
>> but I am still trying to understand it.
>>
>> thanks for a pointer
>>
>> Jeremy
>>
>>
>>
>> --
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>> registered Office: Cain Road, Bracknell, Berks RG12 1HN
>> Registered No: 690597 England
>>
>>
> 

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Received on Wednesday, 30 May 2007 18:09:20 GMT

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