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Re: Intersection of properties?

From: Jeff Thompson <jeff@thefirst.org>
Date: Mon, 04 Aug 2008 16:08:08 -0700
Message-ID: <48978BD8.6020509@thefirst.org>
To: Michael Schneider <schneid@fzi.de>
CC: public-owl-dev@w3.org

Please forgive my naive question as I try to clarify: If I published an ontology
with a million axioms, I used OWL because it is decidable so that a rules engine
examining the ontology won't choke.  BUT before I published the ontology I
made sure that it didn't have any contradicting statements.  What rules engine
did I use to do THAT?  And I ran that rules engine to check for contradictions
without worrying that it would choke, even though the ontology has a million axioms.
So, either
   1) it is a decidable (terminating) problem to determine if an ontology has
contradictions, or
   2) it is not decidable so I have to just publish my ontology not knowing if
it has contradictory assertions and just hope for the best.

I suspect 1) is the truth.  Am I wrong?  Aren't people using some tool or another
to check for contradictions in their ontology?  And why can't these rules used by this
tool be expressed in the ontology itself?

Michael Schneider wrote:
> Jeff Thompson wrote:
>> Here is my pressing issue.
>> The OWL language goes to great lengths to be monotonic and decidable,
>> but cannot express what to do with contradictions.  For example:
>> DisjointClasses(Human, City)
>> ClassAssertion(Washington, Human)
>> ClassAssertion(Washington, City)
>> Contradictions like this are inevitable.  For me to be able to use OWL
>> without
>> needing to extend it with an external rules language, an OWL ontology
>> needs to be expressive
>> enough to say what to do if someone inserts a contradictory assertion.
>> This is such an obvious "use case" that it may be been talked to death
>> already.
>> Will some future version of OWL be expressive enough to give a rule for
>> resolving
>> contradictions?
> That's a different notion of "expressiveness" as what I normally associate
> with a language such as OWL. OWL is based on classical logic, but what you
> are asking for isn't. I don't expect the core language of OWL to follow this
> direction in the future. However, OWL might grow into a whole set of related
> languages, where some of them are non-classical, who knows... 
> For the moment, it may or may not be interesting for you to have a look at
> Pronto:
>   <http://pellet.owldl.com/pronto>
> This Pellet extension provides probabilistic reasoning. I didn't yet find
> the time to look deeper at it, but adapting your example above, I guess you
> could express assertions like:
>   * Washington is a Human with prob = 45%
>   * Washington is a City with prob = 75%
> Now, the result wouldn't be a real contradiction anymore, but only wrong
> with a certain (well defined) degree of probability.
> But I'm not sure that this is a valid example for Pronto. Bijan can (and
> certainly will! :)) tell you more.
> Cheers,
> Michael
> --
> Dipl.-Inform. Michael Schneider
> FZI Forschungszentrum Informatik Karlsruhe
> Abtl. Information Process Engineering (IPE)
> Tel  : +49-721-9654-726
> Fax  : +49-721-9654-727
> Email: Michael.Schneider@fzi.de
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Received on Monday, 4 August 2008 23:08:52 UTC

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