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Re: Question about Extensional Entailment Rules

From: Nick Bassiliades <nbassili@csd.auth.gr>
Date: Thu, 26 Aug 2004 12:01:54 +0300
Message-ID: <412DA702.30608@csd.auth.gr>
To: Jan Grant <Jan.Grant@bristol.ac.uk>
CC: www-rdf-comments@w3.org
Jan Grant wrote:

>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.
>
>  
>
However, the above scenario is already covered by existing entailment rules:
IF
    1) X uni:teaches Y .   &
    2) uni:teaches rdfs:domain uni:faculty . &
    3) uni:faculty rdfs:subClassOf uni:staff .
THEN
    4) X rdf:type uni:faculty . (due to (1) & (2) and rule rdfs2)
&
    5) X rdf:type uni:staff .  (due to (4) & (3) and rule rdfs9)

I am not sure why rule ext1 is necessary, since it is subsumed by the 
two other rules.

Nick

   

-- 
*********************************************************************
* Dr. Nick Bassiliades, Assistant Professor                         *
* Dept. of Informatics, Aristotle University of Thessaloniki        *
* 54124 Thessaloniki, Greece                                        *
*                                                                   *
* Tel: +302310997913   E-mail: nbassili@csd.auth.gr                 *
* Fax: +302310998419   URL: http://lpis.csd.auth.gr/people/nbassili *
*********************************************************************



Received on Thursday, 26 August 2004 09:00:41 UTC

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