- From: Dan Connolly <connolly@w3.org>
- Date: Wed, 29 Oct 2003 17:52:11 -0600
- To: Ian Horrocks <horrocks@cs.man.ac.uk>
- Cc: Jeremy Carroll <jjc@hpl.hp.com>, www-webont-wg@w3.org
On Wed, 2003-10-29 at 17:37, Ian Horrocks wrote: [...] > The case where an ontology forces Thing to be empty is clearly a > special case, and we have to decide whether such an ontology should be > considered consistent. There are good reasons why it should NOT be > considered consistent (the standard treatment in DL and FOL): > > - If such an ontology is consistent, then the axiom A implies not A is > consistent. > > - If such an ontology is consistent, then we can have a situation > where all classes, including Thing, are inconsistent, yet the ontology > is still consistent (unfortunately we don't explicitly state in our > documents what it means for a class to be consistent w.r.t. an > ontology, but the standard definition is that there is some model of > the ontology in which the class has a non-empty extension). That seems fairly relevant to real-world use of OWL. Good enough for me. I second the proposal to require that OWL DL interpretations have non-empty universes. > - If such an ontology is viewed as a FO theory, then the theory > entails false. > > - If such an ontology is viewed as a DL knowledge base, then the KB is > inconsistent. > > > If we want such ontologies to be considered inconsistent, as I am > arguing, then the easiest (and standard) way is simply to change the > definition of what constitutes a model (by insisting that the universe > be non-empty). This would involve minimal changes to the S&AS document > and a change to one test case. -- Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Wednesday, 29 October 2003 18:56:27 UTC