- From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
- Date: Thu, 30 May 2002 11:35:58 -0400
- To: jjc@hplb.hpl.hp.com
- Cc: www-webont-wg@w3.org
From: "Jeremy Carroll" <jjc@hplb.hpl.hp.com> Subject: RE: DTTF: darkest africa Date: Thu, 30 May 2002 16:25:43 +0100 > > > > > Huh? You are now saying that the behaviour of OWL graphs that include > > > > ex:person owl:sameClassAs owl:ABCDEF > > > > is undefined? Why? What is wrong with this? > > The most obvious thing wrong with that is there is no such owl property > as owl:ABCDEF. We control the namespace and we haven't made such a > property. But how does that prevent some other agent from using that URIref? Why is owl:ABCDEF not (a QName that expands into) a valid URI that can be used in OWL? I don't see any hint that the working group is going to ``control'' the owl namespace to this extent. > For the names we do define, the only thing wrong with it (IMO) is that > it gives a misleading impression of what an OWL implementation will or > will not do. If I say > ex:Rest owl:sameClassAs owl:Restriction . > > and then try and use ex:Rest just like owl:Restriction then it won't > work because: > i) the OWL model theory > and > ii) OWL implementations > are looking for syntactic structures with a triple like > > _:foo rdf:type owl:Restriction . > > rather than doing a least fixed point or something like that on the > interpretation of owl:Restriction. > (I don't particularly like doing it syntactically. However I believe we > are not wanting to support two steps in semantic inference. I think it > is straight forward to simply ban some triples to block off any > misapprehension that it may be possible to have indirect impact on the > user level ontology using entailments over OWL concepts. Moreover I > believe that such a banning can be done in a way that postpones the > research issues, rather than prematurely closing them in the negative). Well, my point was precisely that owl:ABCDEF is *not* part of the ``built-in'' OWL machinery, so why should it matter what users do with it? I agree that messing with the OWL built-ins is a dangerous thing to do. > > > I suspect my list is incomplete, the rules for > > > completing it are: > > > - when in doubt add the triple > > > - the only reason for not adding the triple is > > > + it seems genuinely useful > > > and > > > + it expresses something that can be expressed > > > in mainstream description logic. > > > I am assuming that the List vocabulary is in the > > > owl namespace. Otherwise it would need to be > > > explicitly treated in the black list. > > > > I don't understand this rationale for making triples dark. I don't > > understand the rationale for identifying triples as dark in > > this way. I > > don't understand the implications here of making triples dark. > > I am trying to build a fence. The classes and properties and > restrictions still end up as in the domain of discourse, like in RDFS; > but all the abilities of OWL and RDFS to say anything about them at a > meta level is switched off (other than appropriate use of > rdfs:subClassOf between user level classes etc). > > > Of course, we could address the RDFS layering issue > > > simply by deciding that all the dark graphs identified > > > above are contradictions. Then we would respect all > > > their RDFS entailments (trivially). I wouldn't like > > > that much but could live with it, and would prefer it > > > to making RDF Model Theory non-normative. > > > > Huh? > > The suggestion that OWL treat some triples as not having their RDFS > meaning is a suggestion that the RDFS Model Theory is in essence > optional. But why make them contradictions? > > > If we wanted to stress conformance with RDFS then > > > we would have slightly different text > > > > > > [[[ > > > implementation may treat a dark graph as > > > having its RDFS entailments and any others > > > of the implementation's chosing. The simplest > > > implementation is to treat a dark graph as > > > self-contradictory. > > > > > > ]]] > > > > > > (I doubt there would be group consensus for that). > > > > > > If we wished to stress the dangers of paradox we > > > would have text > > > > > > [[[ > > > implementors should note that at least some > > > dark graphs appear self-contradictory in > > > interesting ways e.g. > > > testA, testB, testC > > > ]]] > > > > > Jeremy > > > > I don't think that this proposal can lead to a solution of > > the layering > > paradoxes. I certainly don't see any such solution above. > > No. It doesn't intend to. Then what is it trying to do? > It tries to indicate that we may be able to agree on what we agree on, > and identify the areas where we disagree. The areas where we disagree > are less important than the areas where we agree. There may be practical > ways of avoiding paradox by substantially reducing the apparant power of > the language for describing itself. I don't think there are any > implementations yet that would allow us to use this power. > We have no use cases for exploiting that power. Personally I don't want > to rule that power out for ever, but I believe that I agree with you on > the meaning of all RDF graphs that do not contain any of the triples I > identified. Well, we disagree on the meaning of just about everything in an ontology, including things like John a [intersectionOf A B] . so I don't see how ruling out misuses of OWL vocabularly will help the situation too much. > Also, areas where we disagree can be labelled as such. It is not a three > valued logic but simple practical expediency. I am sorry I was less than > precise about interpretations and truth, I got the impression that you > had understood what I was getting at though. If you don't want to consider triples that misuse the OWL vocabularly, then why not just make them syntactically invalid? I would view that as very much clearer and cleaner. > Jeremy peter
Received on Thursday, 30 May 2002 11:36:49 UTC