- From: Ian Horrocks <horrocks@cs.man.ac.uk>
- Date: Wed, 12 May 2004 01:08:36 +0100
- To: Pat Hayes <phayes@ihmc.us>
- Cc: Stephen Rhoads <rhoadsnyc@mac.com>, www-rdf-logic@w3.org
On May 11, Pat Hayes writes: > > >On May 7, Pat Hayes writes: > >> > >> >For those who didn't follow the debates on the webont mailing list, I > >> >should perhaps draw your attention to the sad history of Pat's morbid > >> >obsession with DLs. I had hoped that having recognised the problem [1] > >> >(the first and hardest step) he would by now be well on the road to > >> >recovery. Sadly, it would appear that this is not the case. In fact > >> >this is not Pat's first relapse [2], so perhaps we shouldn't be > >> >surprised. > >> > > >> >Ian > >> > > >> >[1] http://lists.w3.org/Archives/Public/www-webont-wg/2002Sep/0411.html > >> >[2] http://lists.w3.org/Archives/Public/www-webont-wg/2002Dec/0092.html > >> > >> Perhaps also not uncharacteristically, Ian manages to simultaneously > >> be insulting, offensively ad-hominem and to mislead the unwary > >> reader. The acknowledgement in [1] was to a completely unrelated > >> misunderstanding arising in part from my reaction to an extended > >> series of memoranda claiming to show that (what is now called) > >> OWL-Full was impossible, by a specious reference to the set-theoretic > >> paradoxes, but also in part, I concede, from my own ignorance of DL > >> metatheory at that time. The opinions I expressed in [2] are > >> unrelated to [1] , are not a 'relapse' - to acknowledge that DLs are > >> a subset of FOL is not to endorse the basing of the entire SW effort > >> on that subset - and I still hold them, and will continue to hold > >> them. > >> > >> I won't react to such jibes in future, but the record should be > >>set straight. > > > >Strangely enough, that is exactly what I told myself when I read your > >initial email. > > > >The point I was trying to make with my [witty banter|vile character > >assassination]* is that, amusing though your ritual DL bashing is, it > >obscures the fact that the restriction being discussed here, i.e., not > >being able to create a subPropertyOf rdf:type, is nothing to do with > >DLs per se, but is required in order to keep the language inside what > >I think we agreed to call "conventional" FOL. > > I disagree. rdf:type is simply a binary relation. It happens to be > related to the operation of unary predication in a systematic way, > which can be expressed in SCL-FOL (though not using a syntax that you > would honor with the term 'conventional') by the axiom > > (iff (rdf:type x y) (y x) ) > > and in a more conventional syntax by the axiom > > (rdf:type x y) iff (holds y x) > > but the special nature of this axiom does not affect the fact that > rdf:type is a binary relation. To amplify the point, the operation of > creating a subproperty of rdf:type is quite meaningful and has some > obvious first-order consequences, such as (using SCL notation and > omitting universal quantifiers) > > (iff (rdf:type x y) (y x) ) ...1 (RDF axiom) > (subProperty foo rdf:type) ...2 > (implies (subProperty x y) (implies (x z u) (y z u))) ....3 (RDFS axiom) > (foo thing class) ...4 > |= > (class thing) > > proof: > (implies (foo z u) (rdf:type z u) ) ....5 (3, UInstance; 2, Modus Ponens) > (rdf:type thing class) ...6 (5, Uinstance; 4, Modus Ponens) > (class thing) (1, conj; Uinstance; 6, Modus Ponens) > > Or you could derive it by unit resolution once the implications and > iff were translated into clauses in the usual way. The only thing > unconventional about this is that it systematically suppresses the > 'holds' relation by allowing variables to occur in predicate > position, which does not significantly affect any of the FO > metatheory. I am aware of the conjecture that there is a satisfiability preserving transformation from an OWL-Full ontology into a "conventional" FOL theory. I have yet to see any proof of the correctness of this transformation. Ian > My 'DL police' [witty banter|vile character assassination]* was a > reference to the fact that OWL-DL (hence the "DL") has been > thoroughly checked and constrained so as to not permit a range of > modes of expression, and that if something appears to be > syntactically illegal by virtue of these rules, the chances of one > being able to wriggle past the constraints by some superficial > transformations, as Stephen had suggested, are vanishingly low. This > remark was in part a testament to the thoroughness of the job done by > you and Peter in defining the OWL-DL syntactic conditions, in fact. > As you point out, not all these restrictions arise from the need for > OWL-DL to be a description logic. Nevertheless, for whatever reason, > they have been imposed on the language, and I do not think it is > misleading to imply that they were imposed largely at the behest of > those who were most enthusiastic about DLs. > > >In fact separating the > >syntax of the language from the domain of discourse is fundamental to > >most logics. > > I agree; however, this has nothing to do with the topic. The point is > that there can be systematic alternative representations of the same > fact within a single syntax. This is an elementary truism about > logics of any reasonable expressivity, and is one of the reasons we > have notions like "normal form". > > Pat > > > > >Ian > > > >* delete as appropriate > > > > > > > >> > >> Pat > >> > >> > > >> >On May 7, Pat Hayes writes: > >> >> > >> >> >I realize that everyone is probably beat from that "Classes as > >> >> >Values" discussion in the SWBP, but ... no thoughts on this? > >> >> > > >> >> >Would it be unthinkable to create a subPropertyOf rdf:type? > >> >> > >> >> Its explicitly forbidden in OWL-DL by edict of the DL police, but it > >> >> makes perfect semantic sense and could be done in OWL-Full. On the > >> >> other hand, why not just use rdf:type? What do you gain from the > >> >> explicit subpropertying? > >> >> > >> >> If you thought to sneak past the DL syntax restrictions, forget it. > >> >> The DL police have already thought of all the tricks you could use > >> >> and blocked all the exits. > >> >> > >> >> Pat > >> >> > >> >> >Something like ... > >> >> > > >> >> ><owl:ObjectProperty rdf:ID="hasGenre"> > >> >> > <rdfs:subPropertyOf rdf:resource="&rdf;type"/> > >> >> ></owl:ObjectProperty> > >> >> > > >> >> ><ex:Song rdf:ID="PurpleHaze"> > >> >> > <ex:hasGenre rdf:resource="&ex;ClassRockMusic"/> > >> >> ></ex:Song> > >> >> > > >> >> >Thus, the Individual "PurpleHaze" is an instance of both Song and > >> >> >ClassicRockMusic. > >> >> > > >> >> >Note that the intent is state class membership, not to say that the > >> >> >"subject" of the Song is a concept denoted by a Class (as in the > >> >> >"Classes as Values" paper). > >> >> > > >> >> >--- Stephen > >> >> > > >> >> > > >> >> >On Apr 24, 2004, at 4:50 PM, Stephen Rhoads wrote: > >> >> > > >> >> >> > >> >> >>Folks, > >> >> >> > >> >> >>There are various parts of my (Media Publishing and Distribtuion) > >> >> >>ontology where I would like to avoid the requirement of "multiple > >> >> >>typing". The objective here is to simplify the ontology and user > >> >> >>interfaces which employ it. > >> >> >> > >> >> >>A user of the ontology should be able to simply declare an > >> >> >>Individual to be a Song, Album, Movie, MovieSeries, > >> >> >>TelevisionProgram, TelevisionSeries, RadioProgram or RadioSeries. > >> >> >>Other important class membership should be inferred by property > >> >> >>values. A TelevisionSeries, for example, could have > >> >> >>"hasSeriesType" of "SeasonalSeries" and thus be a member of that > >> >> >>Class. A Movie could have "hasGenre" of "Drama" and thus be a > >> >> >>Drama. > >> >> >> > >> >> >>The problem is that I can't see how to model this without landing > >> >> >>in OWL Full. Take the following example: > >> >> >> > >> >> >>A sample Class hierarchy: > >> >> >> > >> >> >>Music > >> >> >> ElectronicMusic > >> >> >> PopMusic > >> >> >> RockMusic > >> >> >> ClassicRockMusic > >> >> >> GlamRockMusic > >> >> >> GrungeRockMusic > >> >> >> > >> >> >>And sample Class description: > >> >> >> > >> >> >><owl:Class rdf:ID="ClassicRockMusic"> > >> >> >> <rdfs:subClassOf rdf:resource="#RockMusic"/> > >> >> >> <owl:equivalentClass> > >> >> >> <owl:Restriction> > >> >> >> <owl:onProperty rdf:resource="#hasGenre"/> > >> > > >> <owl:hasValue rdf:resource="#ClassicRockMusic"/> > >> >> >> </owl:Restriction> > >> >> >> </owl:equivalentClass> > >> >> >></owl:Class> > >> >> >> > >> >> >>In other words, if the Individual (a Song or Album) hasGenre > >> >> >>ClassicRockMusic, then it *is* ClassicRockMusic (or at least a > >> >> >>member of a Restriction Class with the same class extension). But > >> >> >>(I think) this puts the ontology into OWL Full because > >> >> >>ClassicRockMusic is being treated as both a Class and an Individual > >> >> >>(I can confirm that Racer will not accept the ontology from Protege > >> >> >>because it is "not in OWL DL"). > >> >> >> > >> >> >>Thoughts? Solutions? > >> >> >> > >> >> >>--- Stephen > >> >> > >> >> > >> >> -- > >> >> --------------------------------------------------------------------- > > > >> IHMC (850)434 8903 or (650)494 3973 home > >> >> 40 South Alcaniz St. (850)202 4416 office > >> >> Pensacola (850)202 4440 fax > >> >> FL 32501 (850)291 0667 cell > >> >> phayes@ihmc.us http://www.ihmc.us/users/phayes > >> >> > >> > >> > >> -- > >> --------------------------------------------------------------------- > >> IHMC (850)434 8903 or (650)494 3973 home > >> 40 South Alcaniz St. (850)202 4416 office > >> Pensacola (850)202 4440 fax > >> FL 32501 (850)291 0667 cell > >> phayes@ihmc.us http://www.ihmc.us/users/phayes > >> > > > -- > --------------------------------------------------------------------- > IHMC (850)434 8903 or (650)494 3973 home > 40 South Alcaniz St. (850)202 4416 office > Pensacola (850)202 4440 fax > FL 32501 (850)291 0667 cell > phayes@ihmc.us http://www.ihmc.us/users/phayes >
Received on Tuesday, 11 May 2004 18:08:25 UTC