- From: Jim Hendler <hendler@cs.umd.edu>
- Date: Thu, 31 Oct 2002 17:05:21 -0500
- To: Ian Horrocks <horrocks@cs.man.ac.uk>, Dan Connolly <connolly@w3.org>
- Cc: Deborah McGuinness <dlm@ksl.stanford.edu>, webont <www-webont-wg@w3.org>
At 3:45 PM +0000 10/31/02, Ian Horrocks wrote: >On October 29, Dan Connolly writes: >> >> On Tue, 2002-10-29 at 18:34, Ian Horrocks wrote: >> > >> > The problem with adding hasValue to OWL Lite is that it wouldn't be >> > Lite any more. The lack of hasValue in Lite is, from an implementation >> > point of view, the main thing that differentiates it from fast - >> > hasValue is very tough to deal with, and is responsible for pushing >> > the worst case complexity of reasoning in fast OWL from ExpTime to >> > NExpTime. >> >> Could you unpack that a bit? >> >> Could you give an example, maybe? > >I'm not sure. This isn't anything to do with reasoning techniques or >specific examples, it is a fundamental property of the logic that >basic inference problems (satisfiability, subsumption, entailment) are >much harder when we add extensionally defined classes (which is what >hasValue amounts to). > >If you want an intuition, it comes down to the loss of the tree(ish) >model property. Without this property, it is very hard to devise >decision procedures that work in a goal-directed way and that know >when they are done. > >Ian Ian - the question arose at the Telecon as to whether this was true for both the IF and the ONLY IF (i.e. hasValue -> X vs X -> hasValue) -- that is, does saying "All Mexican restaurants serve Mexican food" cause the problem if you're not expected to be able to say "all places that serve Mexican food are Mexican restaurants"?? -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 Thursday, 31 October 2002 17:05:36 UTC