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Re: NEWBIE: Property restriction semantics

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Tue, 17 Feb 2004 10:49:26 -0500 (EST)
Message-Id: <20040217.104926.102497927.pfps@research.bell-labs.com>
To: kotsomit@hpclab.ceid.upatras.gr
Cc: public-webont-comments@w3.org

From: "Dimitrios A. Koutsomitropoulos" <kotsomit@hpclab.ceid.upatras.gr>
Subject: Re: NEWBIE: Property restriction semantics
Date: Tue, 17 Feb 2004 17:26:09 +0200

> 
> 
> Let's consider the following modification of Brian's example:
> 
> 
> <owl:Class rdf:ID="Student"/>
> 
> <owl:ObjectProperty rdf:ID="hasGrade">
>  <rdfs:domain rdf:resource="#Student"/>
>  <rdfs:range rdf:resource="#Grade"/>
> </owl:ObjectProperty>
> 
> <owl:Class rdf:ID="FailedStudent">
>  <rdfs:subClassOf rdf:resource="#Student"/>
>  <owl:equivalentClass>  <!-- instead of subClassOf -->
>    <owl:Restriction>
>      </owl:onProperty rdf:resource="#hasGrade"/>
>      </owl:hasValue rdf:resource="#Failed"/>
>    </owl:Restriction>
>  </owl:subClassOf>
> </owl:Class>
> 
> And just assert that Brian isA FailedStudent:
> 
> <FailedStudent rdf:ID="Brian" />
> 
> Would this imply that Brian hasGrade Failed?

Yes.  Note, however, that this inference would also be valid in the
original example.  Note also that your example doesn't make much sense, as
it has lots of unusual consequences.

This is yet another case where the RDF/XML syntax is not helpful, as it
obscures the real semantic relationships.  What you have done is define
FailedStudent as follows


	FailedStudent <= Student
	FailedStudent = hasGrade : Failed

From this you can infer 

	hasGrade:Failed <= Student

i.e., any thing that has a failing grade (perhaps in love, for example)
would be a Student.  What you probably want is

	FailedStudent = Student & hasGrade:Failed

or

	FailedStudent <= Student & hasGrade:Failed

In both these cases

	Brian in FailedStudent

implies

	Brian in hasGrade:Failed


> I would be really happy for any feedback on this!
> 
> Many thanks,
> 
> 
> Dimitris Koutsomitropoulos

Peter F. Patel-Schneider
Received on Tuesday, 17 February 2004 10:49:44 UTC

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