From: Ian Horrocks <horrocks@cs.man.ac.uk>

Date: Thu, 17 Oct 2002 18:39:25 +0100

Message-ID: <15790.62925.811830.310168@merlin.horrocks.net>

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

Cc: www-webont-wg@w3.org

Date: Thu, 17 Oct 2002 18:39:25 +0100

Message-ID: <15790.62925.811830.310168@merlin.horrocks.net>

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

Cc: www-webont-wg@w3.org

There may be pragmatic/implementation reasons to go for implies semantics in all cases: - it can only lighten the burden on implementors as there will be fewer kinds of logical entailment to worry about. - the cost isn't very great as implied functionality, transitivity etc. due to strange constraints on possible models doesn't seem like it would be of great interest. - it would satisfy Pat's complaint that logically entailed range and domain restrictions are positively harmful. Ian On October 15, Jeremy Carroll writes: > > 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. > > Jeremy > > > > > > >Received on Thursday, 17 October 2002 13:39:36 GMT

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