Re: Blank Node Equality Question

From: "Jeremy Carroll" <jjc@hplb.hpl.hp.com>
Subject: RE: Blank Node Equality Question
Date: Mon, 21 Jul 2003 12:08:12 +0200

[...]

> However, the question presupposed a graph and two blank nodes that were
> indistinguishable within it.
> We cannot distinguish these blank nodes on the basis of some other graph
> since only urirefs and literals are global. Thus we cannot rule out
> _:a owl:sameIndividualAs _:b .
> and the twins might in fact be the same person.
> 
> Given the question statement, and assuming the initial graph G is
> consistent, then
> 
> G
> _:a owl:sameIndividualAs _:b .
> 
> is consistent.

Not so.  (At least not in Jeremy's reformulation.)

Consider the following graph

_:a rdf:type owl:Thing .
_:b rdf:type owl:Thing .

ex:foo rdf:type owl:Class .
ex:foo owl:oneOf _:l1 .
_:l1 rdf:type rdf:List .
_:l1 rdf:first _:a .
_:l1 rdf:rest _:l2 .
_:l2 rdf:type rdf:List .
_:l2 rdf:first _:b .
_:l2 rdf:rest rdf:nil .
ex:foo owl:oneOf _:l3 .
_:l3 rdf:type rdf:List .
_:l3 rdf:first _:b .
_:l3 rdf:rest _:l4 .
_:l4 rdf:type rdf:List .
_:l4 rdf:first _:a .
_:l4 rdf:rest rdf:nil .

ex:john rdf:type owl:Thing .
ex:john rdf:type _:r1 .
_:r1 rdf:type owl:Restriction .
_:r1 owl:onProperty ex:p .
_:r1 owl:cardinality "2"^^xsd:NonNegativeInteger . 

ex:p rdf:type owl:ObjectProperty .
ex:p rdf:range ex:foo .

This entails

_:a owl:differentFrom _:b .


Peter F. Patel-Schneider
Bell Labs Research
Lucent Technologies