- From: Jim Hendler <hendler@cs.umd.edu>
- Date: Wed, 29 May 2002 12:24:24 -0400
- To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>, jjc@hplb.hpl.hp.com
- Cc: connolly@w3.org, www-webont-wg@w3.org
At 8:29 AM -0400 5/29/02, Peter F. Patel-Schneider wrote: >From: "Jeremy Carroll" <jjc@hplb.hpl.hp.com> >Subject: RE: DDTF/layering: weak class theory seems good enough (5.3, 5.10) >Date: Wed, 29 May 2002 13:06:07 +0100 > >[snip] > > In OWL1 we can choose to: >> A: not get all the set theoretic entailments we would like, but get the >> layering right >> B: get the set theoretic entailments we would like, but screw the >> layering >> C: take enough time to make a better job on the layering and get all the >> set theoretic entailments >> D: take even longer and get both the layering and the set theoretic >> entailments right. >> >> I think both the last two (C and D) can be postponed until OWL2 (after >> this working group). >> >> I personally prefer prioritizing the layering (A), since set theory is >> easier. >> >> Jeremy > >The question is what is the correct layering. If you mean a same-syntax >extension, then, again, that is impossible for the uppper layers without >going to a very non-standard logic. If, however, you allow syntax >extensions, and I see absolutely no reason not to allow syntax extensions, >then the situation changes completely. (Of course, you are still left with >dealing with the odd parts of RDF.) > >peter Peter - I must admit that I am confused, and I'd like to be straight on this. As I understand the world, the current DAML+OIL semantics is an option, but only if we are willing to live without entailments that many of us think should be there. I base this on the wording in Issue 5.10 which you authored, to wit: >DAML+OIL semantics (both the model theory and the axiomatization) >are too weak. For example, it does not allow the inference of >membership in any restrictions that are not present in the knowledge >base, even though many of these are desirable consequences. For >example, if John is an instance of both Person and Employee, >DAML+OIL does not sanction the conclusion that John is an instance >of an intersection of Person and Employee. I took this to mean that one option we have is to live with these weak semantics by saying we give up on desirable consequences (that is - if we rule this issue as POSTPONED we would tacitly be accepting this solution). This is also how I read your earlier document, the layering proposal, and is what you presented at the first f2f -- this is all summed up in note you produced at the last f2f which stated: > >If the WebOnt language is to >> 1/ use RDF syntax, and >> 2/ be an extension of RDF, and >> 3/ to be able to entail appropriate class memberships, >>then the WebOnt language needs to have a facility for having RDF triples >>that do not denote in the RDF model theory (a.k.a. dark triples) and URI >>references that do not denote in the RDF model theory (e.g., URI references >>that only exist in dark triples). > which I take to mean that we could have 1 and/or 2, but not 3. In the message above, you claim we cannot do it by accepting these weak semantics, which seems to contradict my previous understanding. PLEASE NOTE - I AM NOT EXPRESSING AN OPINION ON THIS - I just want to make sure that I (and the WG) have a handle on this -- -JH -- Professor James Hendler hendler@cs.umd.edu Director, Semantic Web and Agent Technologies 301-405-2696 Maryland Information and Network Dynamics Lab. 301-405-6707 (Fax) Univ of Maryland, College Park, MD 20742 240-731-3822 (Cell) http://www.cs.umd.edu/users/hendler
Received on Wednesday, 29 May 2002 12:30:35 UTC