- From: Jos De_Roo <jos.deroo@agfa.com>
- Date: Tue, 21 Jan 2003 14:24:24 +0100
- To: "Jeremy Carroll <jjc" <jjc@hpl.hp.com>
- Cc: www-webont-wg@w3.org, www-webont-wg-request@w3.org
> I have made, a possibly successful, case to my HP colleagues that OWL is about > documents: > - syntactic forms > - semantic consistency > > The WG seemed minded to restrict our concerns to precisely those when it came > to specifying software. In particular there was no desire to specify any more > complicated reasoning component, such as one that could actually run our > entailment tests. > > So we have: > - a semantics that permits discussion of the meaning of a single document > (specifically its consistency) > - a semantics that permits discussion of the relationship between two > documents (entailment) > - three syntactic levels > > What I have heard we want to have as CR exit criteria is adequate exploration > of the first and third of these; and not much on the second. > > This could possible be better reflected by making the entailment part of the > semantics informative rather than normative. I don't see why, but I read further... > Possible text near the beginning of the AS&S: > [[ > OWL specifies an RDF vocabulary and three syntactic levels: OWL Lite, OWL DL, > OWL Full, each of which specifies a set of RDF documents. OWL normatively > specifies through the use of model theoretic semantics the consistency of any > such document. The model theoretic semantics also permits the discussion of > entailment relationship between pairs of documents. These relationships are > informative. In particular, implementors of OWL Consistency Checkers are free > to use alternative semantics as long as these are logically equivalent to an > OWL Consistency Checker built using the semantics specified here. No other > constraints on the semantics of OWL implementations are normatively > specified. > ]] > > (with appropriate 'normative' and 'informative' markers elsewhere) > > The motivation here is that much of the difficulty HP has with the current > specification of OWL is to do with what is expected of OWL implementations, > and an apparent mismatch between that and the sketch of CR exit criteria > created at the f2f. Specifically we do not intend to migrate Jena to the OWL > Semantics any time soon, nor do we see competing systems planning such a > migration either; nor do we see a WG intending to make the migration of such > a system to OWL (and its semantics) a CR exit criterion. hm.. is certainly a reasonable step for the roadmap and above "second" could be a second step my experience though is that e.g. proving inconsistencies is not easier than the "second" > To give a specific example, the comprehension principle is part of OWL > semantics, i.e. that various classes and restrictions necessarily exist. > These can be turned into consistency tests at the OWL Full level but not at > OWL DL or OWL Lite. e.g. > > <owl:Restricition> > <owl:onProperty> > <owl:ObjectProperty rdf:ID="p"/> > </owl:onProperty> > <owl:hasValue> > <owl:Thing rdf:ID="v"/> > </owl:hasValue> > <rdf:type> > <owl:Class> > <owl:complementOf rdf:resource="&owl;Class"/> > </owl:Class> > </rdf:type> > </owl:Restriction> > > This says that a particularly restriction is not an OWL Class, and this is > inconsistent. > This: > (a) seems plausibly straight forward to implement (I wouldn't be surprised if > Euler already could prove this) well, we now can... { <http://www.agfa.com/w3c/euler/owl-rules#rule20c2> . _:905719_1 owl:complementOf owl:Class. _:905719_1 a owl:Class} log:implies {_:905719_1 log:inconsistentWith owl:complementOf}. > (b) is anyway in OWL Full where we are being explicit about the lower > implementability goals. > > The alternative OWL DL entailment: > > <owl:ObjectProperty rdf:ID="p"/> > <owl:Thing rdf:ID="v"/> > > DL-entails > > <owl:Restricition> > <owl:onProperty> > <owl:ObjectProperty rdf:ID="p"/> > </owl:onProperty> > <owl:hasValue> > <owl:Thing rdf:ID="v"/> > </owl:hasValue> > </owl:Restriction> > > seems to present more difficulty, particularly in a forward chaining > environment, and the WG does not seem minded to want to see even one complete > OWL DL reasoner that could do this before exiting CR. right, I don't know how to solve that one and I also note that all our 7 "no proof found" ones have to do with lack of comprehesion > (I note that a unionOf example would be a lot less compelling, partly because > both the entailment and the inconsistent file are at the same OWL DL level) -- , Jos De Roo, AGFA http://www.agfa.com/w3c/jdroo/
Received on Tuesday, 21 January 2003 08:29:34 UTC