- From: Pat Hayes <phayes@ihmc.us>
- Date: Sat, 10 Nov 2007 09:22:17 -0600
- To: "Michael Schneider" <schneid@fzi.de>
- Cc: "Owl Dev" <public-owl-dev@w3.org>, <alanruttenberg@gmail.com>
>[Comment to OWL-WG discussion; CC'ed to involved WG members] > >Hi OWL-DEV list! > >I just found the following mail by Alan Ruttenberg on the OWL-WG list > > Re: ISSUE-3: REPORTED: Lack of anonymous individuals > http://lists.w3.org/Archives/Public/public-owl-wg/2007Nov/0214.html > >where he notices that bNodes are used in both the RDF mapping for OWL-1.0 >and for OWL-1.1, and Alan asks what consequences it would have to drop >bNodes from OWL-DL. Alan's question brought a related question up to my >mind, which I present below. > >BTW: No one has to read the complete thread there about "anonymous >individuals", my question doesn't depend on this discussion and is >self-contained. > >Now my question: > >OWL-DL-1.0 allows me to state that a class :C is the intersection of classes >:D1 and :D2. When I have to write such an axiom in RDF syntax, I generally >do it by means of Turtle in the following way: > > (1) :C a owl:Class . > (2) :D1 a owl:Class . > (3) :D2 a owl:Class . > (4) :C owl:equivalentClass [ a owl:Class ; > owl:intersectionOf ( :D1 :D2 ) > ]. > >where (4) is just a convenient Turtle shortcut for writing > > (4a) _:X a owl:Class . > (4b) :C owl:equivalentClass _:X . > (4c) _:X owl:intersectionOf ( :D1 :D2 ) . > >So we actually have a bNode "_:X" in our OWL-DL-1.0 ontology above. Note however that you could have done a translation with a URIref instead of a bnode (invent some random "skolem" URI for the purpose) > >Now OWL-DL-1.0 has both a "direct semantics" and an "RDF compatible >semantics", and for the DL sublanguage of OWL-1.0 they are intended to be >equivalent. This allows me to interprete the above OWL-DL-1.0 ontology by >using RDF compatible OWL-DL semantics. And because bNodes are interpreted in >RDF as /existential variables/, the meaning of axiom (4) is (in natural >language): > > "There exists some class ?X, > to which class :C is equivalent, > and which is the intersection of the classes :D1 and :D2." > >So this statement is actually a quantification about a /class/ variable. But >I thought that OWL-DL was a First Order Logic dialect, where all universal >and existential quantifications must be asserted about /individual/ >variables only? Well, just for clarification, OWL-Full and RDFS are also first-order, but allow quantification over classes. One can quantify over reasonably-sized universes of classes (or indeed anything else) in first-order frameworks. (What one cannot quantify over is the set of all mathematically definable classes, but nobody wants to do that.) But your point can still be made, since OWL-DL is a *segregated* first-order language which does not permit individuals and classes to be intermixed, and prohibits quantification over the latter. But see below. >And in an RDF-mapped OWL-DL-1.0 ontology, I am not allowed >to regard such a class variable as an individual variable, because in OWL-DL >the OWL universe is strictly separated. True, but what is the problem? That variable only arises in the RDF translation: it is not a variable in OWL-DL itself. The direct semantic meaning of the intersection statement is clear, and mentions three classes. The RDF meaning of the OWL/RDF is also clear, and also mentions (the same) three classes, but uses two names (the URI ":C" and the bnode) to refer to one of them. So? The fact that the RDF uses a name in a way that is syntactically prohibited in the DL says nothing about their semantic equivalence. Pat >So this looks to me like a problem >for the intended equivalence between Direct Semantics and RDF Compatible >Semantics for OWL-DL. > >There is certainly some misunderstanding on my side, but maybe someone can >clarify? > >Cheers, >Michael > >-- >Dipl.-Inform. Michael Schneider >FZI Forschungszentrum Informatik Karlsruhe >Abtl. Information Process Engineering (IPE) >Tel : +49-721-9654-726 >Fax : +49-721-9654-727 >Email: Michael.Schneider@fzi.de >Web : http://www.fzi.de/ipe/eng/mitarbeiter.php?id=555 > >FZI Forschungszentrum Informatik an der Universität Karlsruhe >Haid-und-Neu-Str. 10-14, D-76131 Karlsruhe >Tel.: +49-721-9654-0, Fax: +49-721-9654-959 >Stiftung des bürgerlichen Rechts >Az: 14-0563.1 Regierungspräsidium Karlsruhe >Vorstand: Rüdiger Dillmann, Michael Flor, Jivka Ovtcharova, Rudi Studer >Vorsitzender des Kuratoriums: Ministerialdirigent Günther Leßnerkraus -- --------------------------------------------------------------------- IHMC (850)434 8903 or (650)494 3973 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32502 (850)291 0667 cell phayesAT-SIGNihmc.us http://www.ihmc.us/users/phayes
Received on Saturday, 10 November 2007 15:22:43 UTC