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Re: Question about Extensional Entailment Rules

From: Jan Grant <Jan.Grant@bristol.ac.uk>
Date: Thu, 26 Aug 2004 09:48:05 +0100 (BST)
To: Nick Bassiliades <nbassili@csd.auth.gr>
cc: www-rdf-comments@w3.org
Message-ID: <Pine.GSO.4.61.0408260945150.17591@mail.ilrt.bris.ac.uk>

On Thu, 26 Aug 2004, Nick Bassiliades wrote:

> Hi all,
> 
> I would like to ask you whether I am missing something from the extensional
> entailment rules ext1&2
> in the RDF Semantics document (http://www.w3.org/TR/rdf-mt/).
> 
> Rule ext1 says that when:
>   uuu rdfs:domain vvv .
> and
>   vvv rdfs:subClassOf zzz .
> are true, then the triple:
>   uuu rdfs:domain zzz .
> should be added.
> 
> However, IMHO this looks rather bizarre! This rule states that when a property
> has a certain class as a
> domain, it must also have all its superclasses as a domain. I believe that
> it's the other way around:
> all the subclasses of a class can be domains for the property uuu.
> 
> For example,
>   uni:faculty rdfs:subClassOf uni:staff .   (/Faculty members are member of
> the staff/)
>   uni:teaches rdfs:domain uni:faculty .     (/Faculty members teach/)
> then we infer with rule ext1 that:
>   uni:teaches rdfs:domain uni:staff .       (/All members of the staff can
> teach!/)
> 
> I would expect it to work the other way around:
>   uni:lecturer rdfs:subClassOf uni:faculty .   (/Lecturers are //Faculty
> members/)
>   uni:teaches rdfs:domain uni:faculty .        (/Faculty members teach/)
> then we infer that:
>   uni:teaches rdfs:domain uni:lecturer .       (/Lecturers // can teach/)
> 
> Am I missing something here?

The semantics are conjunctive. To say that "the domain of uni:teaches is 
uni:faculty" means, if you have statements of the kind
	X uni:teaches Y .
then X must be a member of uni:faculty: we can infer that about its 
type. What we can't do is infer that X is a uni:lecturer; but we _can_ 
logically infer that X must also be a member of uni:staff. The rules for 
domain and range are universally quantified in this fashion, so whilst 
it looks odd it's right.

-- 
jan grant, ILRT, University of Bristol. http://www.ilrt.bris.ac.uk/
Tel +44(0)117 9287088 Fax +44 (0)117 9287112 http://ioctl.org/jan/
( echo "ouroboros"; cat ) > /dev/fd/0 # it's like talking to yourself sometimes
Received on Thursday, 26 August 2004 08:48:40 UTC

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