From: Jeremy Carroll <jjc@hpl.hp.com>

Date: Tue, 15 Oct 2002 23:22:55 +0200

To: www-webont-wg@w3.org

Message-Id: <200210152322.55728.jjc@hpl.hp.com>

Date: Tue, 15 Oct 2002 23:22:55 +0200

To: www-webont-wg@w3.org

Message-Id: <200210152322.55728.jjc@hpl.hp.com>

Summary: attempt to collect arguments about this issue. (Also added justification for uniformity, and a new argument about mutually entailing ontologies). >Range >Domain(P,C) implies/iff (forall x,y P(x,y) -> C(x)) >TransitiveProperty(P) implies/iff (forall x,y,z (P(x,y) ^ P(y,z)) -> P(x,z)) >SymmetricProperty(P) implies/iff (forall x,y P(x,y) -> P(y,x)) >FunctionalProperty(P) implies/iff (forall x,y,z (P(x,y) ^ P(x,z)) -> y=z) >InverseFunctionalProperty(P) implies/iff (forall x,y,z (P(y,x) ^ >P(z,x)) -> y=z) >inverseOf(P,Q) implies/iff (forall x,y P(x,y) -> Q(y,x)) I hear Dan, Jos, myself, Peter and Ian being able to go either way here. There seem to be various arguments: - treat them all the same (unarticulated) Less difficult for implementors,. less difficult to document, less difficult to learn. I suspect the Guide would be shorter with iff semantics. - implies only Few implementation would actually implement iff. (However most of the implementors in the group seem to have come round to the possibility of implementing iff) - natural usage Pat (so far unsupported) has opinions about natural usage that split domain, range and inverse off as intensional (implies) and the others as extensional (iff). - rdf datatyping I think this argument is now dead - some versions of rdf:datatyping requried intensional reading of rdf:range. - possibility of identifying identical ontologies (new argument) With extensional semantics then ontologies using these with identical semantics entail one another. With intensional semantics then it is not the case e.g. <owl:FunctionalPropery rdf:ID="a"> <owl:inverse rdf:resource="#b" /> </owl:FunctionalProperty> <owl:InverseFunctionalPropery rdf:ID="b"> <owl:inverse rdf:resource="#a" /> </owl:InverseFunctionalProperty> either have identical meaning or not. Seems potentially useful, to say that they do have identical meaning. - argument by authority iff we take this style of argument seriously - surprising entailments An empty property is necessarily transitive, functional, inversefunctional, its own inverse, etc. I think consistency is what I feel strongly about. JeremyReceived on Tuesday, 15 October 2002 17:24:42 UTC

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