- From: Jeremy Carroll <jjc@hplb.hpl.hp.com>
- Date: Thu, 29 Aug 2002 07:26:04 +0200
- To: <www-webont-wg@w3.org>
Having looked through Pat's latest: http://www.coginst.uwf.edu/users/phayes/RDFS2OWL-D.html I believe that it goes a very long way to reconciling, Peter's http://www-db.research.bell-labs.com/user/pfps/owl/semantics.html and the RDF(S) model theory. While this is certainly worth a big cheer, I am not ready to celebrate by closing off as many issues as Peter would like. Nor is it clear that Pat's work, which shows sufficient compatibility between the RDF(S) approach and the Description Logic approach, necessarily results in the group chosing the DL approach (Peter's MT) as normative, and Pat's as non-normative support. I think it may be helpful to formally record some decision that progress is being made, I will think a bit more and try and suggest a substantial weaker proposal that I could support. This may partly be about speed of closure. In terms of process, if the WG feels that Peter's proposals for how to address OWL semantics are the way to go, I would prefer a decision to publish WDs showing that semantics followed by community feedback, and then the formal decisions that close the associated issues. I will try and indicate here some of the issues that I think merit further discussion. > Issue 4.6 equivalentTo I think there are other resolutions to this than simply deleting equivalentTo. I would prefer dropping all the sameXXXAs and keeping equivalentTo. This could remain strongly typed so that xx rdf:type owl:Object . yy rdf:type owl:Class . xx owl:equivalentTo yy . is a contradiction. I also am increasingly believing that there are positive advantages in having the syntactic expressions in the domain of discourse (which is the case in Pat's approach). Thus issues about intensional and extensional sameClassAs are not, at least for me, resolved by Pat's work. What Pat as shown is that the extensional sameClassAs is at least an option which is compatible with RDF(S) model theory. Peter's MT cannot extend beyond the abstract syntax, with it's limitations. Pat's MT is automatically extended beyond that, and explicitly cut back to match Peter's world. Maybe there are areas outside Peter's proposed abstract syntax that would be useful > Issue 5.1 Uniform treatment of literal/data values > There is a strict separation between OWL object and data values. > Removing the separation has computational consequences. We have had some discussion of this, but I didn't feel we reach closure (i.e. consensus that the computational consequences were sufficiently compelling to maintain this separation). I find Dan's same state example a compelling use case and would be happy to have another way of making an OWL reasoner not perform as the cost. > Issue 5.10 DAML+OIL semantics is too weak You and Pat have shown one approach to resolving it. At times both I and Dan have argued that the alternative of simply dismissing this issue, and asserting that the DAML+OIL semantics is actually adequate is also a possible way forward. I personally find Pat's herbrand closure clever, but perhaps too clever. Certainly worth an appendix, but the community might be better served by the weaker semantics ... > Issue 5.19 Classes as instances I suspect that the advocates of this issue will not be pleased to simply have it dismissed. Jeremy
Received on Thursday, 29 August 2002 01:20:47 UTC