- From: Jim Hendler <hendler@cs.rpi.edu>
- Date: Sun, 16 Dec 2007 17:18:32 -0500
- To: Michael Schneider <schneid@fzi.de>
- Cc: "Owl Dev" <public-owl-dev@w3.org>, <pfps@research.bell-labs.com>, <ian.horrocks@comlab.ox.ac.uk>, <alanruttenberg@gmail.com>
- Message-Id: <10CA1D4E-1ABB-47D1-ABF5-845A8098D5C7@cs.rpi.edu>
I have no objection to the solution that was used in OWL 1.0 for this. So far, if a feature adds problems to DL, we apparently throw it out immediately, but if it causes problems to full, we try to find a work around without worrying too much if it cases problems or confusion - I just fine this asymmetry to be troubling. So I propose we don't include QCRs, since the solution proposed is one that was already considered and rejected in OWL 1.0 - what has changed? -JH On Dec 16, 2007, at 4:43 PM, Michael Schneider wrote: > [ public comment to discussion in OWL-WG; > also posted to involved WG members ] > > Jim Hendler wrote on Thu, 13 Dec 2007 > in <http://lists.w3.org/Archives/Public/public-owl-wg/2007Dec/ > 0176.html> > within thread "Re: PROPOSAL to close ISSUE-68" > >> I would not be happy with this solution - it creates yet more, >> seemingly unecessary terms, and it also was, in DAML days, the single >> feature name that confused the most people - I thought we were >> proposing a clean solution that didn't require creating a new >> syntactic feature, this is quite different - so I oppose closing this >> issue with Peter's suggested solution. >> -JH >> >> On Dec 13, 2007, at 11:27 AM, Peter F. Patel-Schneider wrote: >> >>> >>> ISSUE-68 has to do with a nonmonotonicity in the mapping rules for >>> qualified cardinality restrictions. As pointed out in several >>> places >>> this can be alleviated by using the DAML+OIL solution of having a >>> different property for qualified cardinalities. >>> >>> I thus propose using >>> >>> owl:minCardinalityQ >>> owl:maxCardinalityQ >>> owl:cardinalityQ >>> >>> just as in DAML+OIL and close the issue with this change. >>> >>> Peter F. Patel-Schneider >>> Bell Labs Research >>> >>> PS: Just about any name could be used, but this one has historical >>> antecedents. >>> >> >> "If we knew what we were doing, it wouldn't be called research, would >> it?." - Albert Einstein >> >> Prof James Hendler > http://www.cs.rpi.edu/~hendler >> Tetherless World Constellation Chair >> Computer Science Dept >> Rensselaer Polytechnic Institute, Troy NY 12180 > > Hi Jim! > > Peter has already pointed out in another thread a serious problem for > OWL-1.1-Full arising from the current RDF mapping of QCRs: > > QCR problem in OWL 1.1 Full - action ?? from F2F > <http://lists.w3.org/Archives/Public/public-owl-wg/2007Dec/ > 0095.html> > > And I had found a second problem with the same RDF mapping, which > might at > least lead to non-desirable effects: > > <http://lists.w3.org/Archives/Public/public-owl-dev/2007OctDec/ > 0224.html> > > Both problems are easily solved by Peter's proposed change to the RDF > mapping. > > Based on Peter's finding, I want to give an example in this mail, > which > shows what severe consequences it may have for OWL-1.1-Full, if the WG > sticks to the current RDF mapping for QCRs. > > Let's regard the following OWL-1.1-DL ontology in Functional > Syntax, which > makes use of QCRs: > > (A1) SubClassOf(Human ObjectExactCardinality(2 hasBodyPart Leg)) > (A2) SubClassOf(Dog ObjectExactCardinality(2 hasBodyPart Ear)) > (A3) SubClassOf(Dog ObjectExactCardinality(4 hasBodyPart Leg)) > (A4) ClassAssertion(pluto Dog) > > In natural English: > > "A human has exactly two legs as body parts (A1), > while a dog has two ears (A2) and four legs (A3). > There is also some dog named 'Pluto' (A4)." > > It is clear that this ontology will be satisfiable in OWL-1.1-DL. I > will > show that the current RDF mapping of QCRs translates this ontology > into an > RDF graph, which will most likely be *inconsistent* under OWL-1.1-Full > semantics. Note that the above ontology does not look very > contrieved, so I > expect that the problem shown below will hit many OWL-1.1-Full > ontologies. > > Here is my reasoning why the above ontology will probably be > inconsistent > under OWL-1.1-Full semantics: > > The RDF translation for axiom (A1) is, under the current RDF > mapping for > QCRs, given by (leaving out obvious typing triples): > > (R11) <Human> rdfs:subClassOf _:x . > > (R12) _:x rdf:type owl:Restriction . > (R13) _:x owl:onProperty <hasBodyPart> . > (R14) _:x owl:cardinality 2 . > (R15) _:x owl11:onClass <Leg> . > > As Peter has already pointed out, the RDF graph {(R12),(R13),(R14)} is > itself the RDF translation of an *other* OWL construct, which is an > UN-qualified cardinality restriction on property 'hasBodyPart'. For > this sub > graph, there already exists an OWL-1.0-Full semantic condition, > given in > sec. 5.3 of [1], table "Conditions on OWL restrictions", which in > essence is > defined to be: > > (S-CARD) > IF > r owl:onProperty p . > r owl:cardinality n . > THEN > CEXT(r) = { x : card({y: x p y}) = n } > > This semantic condition tells that if there exists an (un-qualified!) > "=n"-cardinality restriction r on some property p in an RDF graph, > then the > /class extension/ of r ("CEXT(r)") equals to the set of all > instances x > which have exactly n ocurrences of property p assigned to them. > > So given that (S-CARD) is reused in OWL-1.1-Full (what I regard to > be very > likely), we will receive from the RDF graph {(R1*)} the following > entailment: > > (E1) CEXT(_:x) = { x : card({y: x hasBodyPart y}) = 2 } > > Now, OWL-1.1-Full will have to contain an additional semantic > condition for > handling QCRs, and I strongly believe that such a semantic > condition will > have the following form: > > (S-QCR) > IF > r owl:onProperty p . > r owl:cardinality n . > r owl11:onClass c . > THEN > CEXT(r) = { x : card({y: x p y AND y rdf:type c}) = n } > > In this case, we will receive the following /additional/ entailment > from the > RDF graph {(R1*)}: > > (E2) CEXT(_:x) = { x : card({y: x hasBodyPart y AND y rdf:type > Leg}) = 2 } > > Taken together, entailments (E1) and (E2) tell that > > (E3) { x : card({y: x hasBodyPart y}) = 2 } > = CEXT(_:x) = > { x : card({y: x hasBodyPart y AND y rdf:type Leg}) = 2 } > > This alone looks odd, and it is in essence, AFAICT, what Peter was > about in > his original mail. However, (E3) alone is still satisfiable under > specific > conditions. > > But let's now look at axiom (A2): With an analog argumentation as > for (A1) > we receive the following set equality: > > (E4) { x : card({y: x hasBodyPart y}) = 2 } > = CEXT(_:y) = > { x : card({y: x hasBodyPart y AND y rdf:type Ear}) = 2 } > > where '_:y' denotes the cardinality restriction used in (A2), after > being > translated into an RDF graph. Note that '_:y' is a different bNode > from > '_:x', so it /may/ denote a different restriction class. > > But looking closer to (E3) and (E4) reveals, that the respective > left hand > sides of these equations are the /same/ in both cases. So we learn: > > (E5) CEXT(_:x) = CEXT(_:y) > > Now, looking again into sec. 5.2 of [1], table "Characteristics of OWL > vocabulary related to equivalence", first entry, we see that the > following > semantic condition holds (please mind the "iff" in the right table > header!): > > (S-EQUIV) > IF > CEXT(x) = CEXT(y), for classes ("IOC") x and y > THEN > x owl:equivalentClass y > ("<x,y> IN EXT_I(S_I(E))" with E := "owl:equivalentClass") > > Thus, from (E5) and (S-EQUIV) we obtain: > > (E6) _:x owl:equivalentClass _:y . > > And this means that the two QCRs from axioms (A1) and (A2) are > actually > equivalent classes. Or in English: > > "Everything which has exactly two ears > also has exactly two legs, and vice versa." > > So axiom (A2) is semantically OWL-1.1-Full equivalent to (in > Functional > Syntax for easy read, but assume it were given in RDF instead): > > (A2') SubClassOf(Dog ObjectExactCardinality(2 hasBodyPart Leg)) > > The QCR in (A2') is obviously disjoint from the QCR in (A3), so > class Dog, > being a subclass of both QCRs, turns out to be empty: > > (E7) <Dog> rdfs:subClassOf owl:Nothing . > > And by stating through (A4) that Pluto is a Dog, we see that our > ontology is > inconsistent in OWL-1.1-Full: > > (E8) <Pluto> rdf:type owl:Nothing . > > > Cheers, > Michael > > [1] OWL S&AS - §5: RDF-Compatible Model-Theoretic Semantics > http://www.w3.org/TR/owl-semantics/rdfs.html > > -- > 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 "If we knew what we were doing, it wouldn't be called research, would it?." - Albert Einstein Prof James Hendler http://www.cs.rpi.edu/~hendler Tetherless World Constellation Chair Computer Science Dept Rensselaer Polytechnic Institute, Troy NY 12180
Received on Sunday, 16 December 2007 22:19:03 UTC