From: pat hayes <phayes@ai.uwf.edu>

Date: Thu, 24 Oct 2002 11:20:13 -0500

Message-Id: <p05111b01b9ddcd494042@[65.217.30.130]>

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

Cc: www-webont-wg@w3.org

Date: Thu, 24 Oct 2002 11:20:13 -0500

Message-Id: <p05111b01b9ddcd494042@[65.217.30.130]>

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

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. But it would fail to satisfy the RDFS requirement that subClassOf and subPropertyOf are transitive. We could of course just add this as an ad-hoc semantic requirement, but that seems very tacky. Given the option between all IF and all IFF, I think the all-IFF option is more coherent. But I would prefer a more tailored solution, as you know. Pat >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 >> >> >> >> >> >> >> -- --------------------------------------------------------------------- IHMC (850)434 8903 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32501 (850)291 0667 cell phayes@ai.uwf.edu http://www.coginst.uwf.edu/~phayesReceived on Thursday, 24 October 2002 12:20:25 GMT

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