- From: Ian Horrocks <horrocks@cs.man.ac.uk>
- Date: Thu, 15 May 2003 22:03:48 +0100
- To: "Smith, Michael K" <michael.smith@eds.com>
- Cc: Jim Hendler <hendler@cs.umd.edu>, Jeremy Carroll <jjc@hpl.hp.com>, www-webont-wg@w3.org
On May 15, Smith, Michael K writes: > > I am happy to add "desirable computational properties" to the > species description of Lite in the Guide. > > But I am a little hesitant regarding "maximal decidable subset, although > subject to a higher worst-case complexity". Has anyone demonstrated > that that DL is the maximal decidable subset of Full? I believe that you are right to be hesitant. It would be difficult if not impossible to prove such a statement - the expressive power of different "subsets" may not even be comparable. I'm not even sure I would describe DL as a subset of Full - it certainly isn't a subset in the usual sense as it has a completely different semantics. Ian >The DL text > currently says: > > > OWL DL supports those users who want the maximum expressiveness > > without losing computational completeness (all entailments are > > guaranteed to be computed) and decidability (all computations will > > finish in finite time) of reasoning systems. > > Which seems to pretty much capture the intent. ?? > > - Mike > > Michael K. Smith, Ph.D., P.E. > EDS - Austin Innovation Centre > 98 San Jacinto, #500 > Austin, TX 78701 > > phone: +01-512-404-6683 > email: michael.smith@eds.com > > > > -----Original Message----- > From: Jim Hendler [mailto:hendler@cs.umd.edu] > Sent: Wednesday, May 14, 2003 7:11 AM > To: Jeremy Carroll; www-webont-wg@w3.org > Subject: Re: Proposed response to Martin Merry, HP > > > > (note - there is a suggestion to editors for some wording changes to > Ref and Guide in this message - it is before the section marked > personal opinion) > > > At 8:44 AM +0300 5/14/03, Jeremy Carroll wrote: > >In > >http://lists.w3.org/Archives/Public/www-webont-wg/2003May/0181.html > > > >DanC: > >> On closer examination of the comment, it seems > >> to be more about what goes in OWL DL than > >> what goes in OWL Lite. > > > >And in ... > >http://lists.w3.org/Archives/Public/www-webont-wg/2003May/0174.html > >DanC: > >>Please help me find the relevant decisions > >>and/or find evidence that those implementations > >>pass some relevant tests and/or add an > >>issue to the issues list. > > > >In January, we agreed a definition of a "complete OWL DL consistency > checker", > >if we had evidence that such a thing existed, and/or that more than one > would > >exist in the future (and the WG was satisfied that they would be > practically > >usable, rather than essentially theoretical exercises) then we could > respond > >with a message that indicated that, and that we thought that that was > >sufficient to justify the DL level. > > > >If we don't have such evidence then I agree with > >http://lists.w3.org/Archives/Public/www-webont-wg/2003May/0181.html > > > >DanC: > >> Mr. Merry's point, "We're concerned that OWL users should have their > >> expectations met when they use OWL compliant systems." seems well > >> made, no? > > > So let's set their expectations correctly -- we did try, by the way - > in Reference, section 8.2 we say: > > In particular, the OWL DL restrictions allow the maximal subset of > OWL Full against which current research can assure that a decidable > reasoning procedure can exist for an OWL reasoner. > > and in 8.3 we say > > The limitations on OWL Lite place it in a lower complexity class than > OWL DL. This can have a positive impact on the efficiency of complete > reasoners for OWL Lite. > > > In fact, my original response to Mr. Merry was going to be that we > had already addressed his comments and point out these quotes --- > However, his comments and a couple of others we received show that we > haven't made the difference clear ENOUGH in our documents. (For > example, in section 1.2 we don't mention the computational issue). I > therefore suggest that editing Ref and Guide to set expectations is > the correct solution - consistent w/WG decisions in the past. > > > One we could fix ref, is to make it clear that the difference between > OWL Lite and OWL DL with respect to this computational issue is > there. For example, when we first introduce Lite in section 1.2 of > ref we say: > > OWL Lite is particularly targeted at tool builders, who want to > support OWL, but want to start with a relatively simple basic set of > language features. > > instead of saying it is known to have a relatively efficient decision > procedure (and citing the literature). Maybe simply adding a > sentence after the one I cite above that says > > "In addition, OWL Lite is designed based to fit into a known > computational class that, while exponential, is lower than the > complexity of OWL DL [cite something]" > > I also think the "Species of OWL" section of the Guide is also less > clear than it could be, and might be wordsmithed to make the issue > clearer (for example, OWL Lite could say "Desirable computational > properties" and OWL DL could say "maximal decidable subset, although > subject to a higher worst-case complexity") > > Guus, Mike S -- would making these edits be acceptable? If so, I > would include in the response to Merry and to the other similar > issues. > > > > <PERSONAL OPINION> > > > >(A danger is that if OWL DL is tainted then the whole OWL brand is > tainted). > >>Jeremy > > What I would say would make OWL DL "tainted" would be to remove oneOf > and hasValue. hasValue is used in about 10% of the ontologies in the > DAML ontology library, and oneOf, although not heavily used in that > library, is IMHO necessary for mapping existing sources into > ontologies --my group has used it in many cases where we have used > either an XML schema or a database schema as the basis of an > ontology, especially in our work with Web Service Composition [1]. I > would also remind the group that we actually had support in the WG to > put hasValue in Lite, but decided not to due to the computational > issue. > > I would argue strongly that it is better to explain things more > clearly in our documents than to change the language. We spent a > long time developing a language that is well balanced for many > considerations, and I'd like to see if used in practice before we > start cutting useful features because of computational issues that > may rarely or never arise in real applications. For instance, > PARKA-DB [2], still the fastest ontology management system deployed > to date, is in the same complexity class as OWL DL, but somehow > people don't seem to mind since it can answer most useful queries in > a few milliseconds against ontologies with tens of thousands of > classes - it has a worst case time that could be in several minutes > for the largest ontologies built yet - but that doesn't seem to > matter since after 5 seconds it asks the user if they want to > continue, and most people say "no" and reformulate the query... > > Quoting one of our comment raisers, speaking about OWL: > > At 11:43 PM -0400 5/9/03, Bijan Parsia wrote in [3]: > 4) Get the damn thing out the door. > > </PERSONAL OPINION> > > > [1] http://www.mindswap.org/papers/composition.pdf > [2] http://www.cs.umd.edu/projects/plus/Parka/aaai97.ps > [3] > http://lists.w3.org/Archives/Public/public-webont-comments/2003May/0069.html > > -- > 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 Thursday, 15 May 2003 17:04:09 UTC