- From: Vaughan Pratt <pratt@cs.stanford.edu>
- Date: Thu, 22 Feb 2007 10:10:47 -0800
- To: semantic-web@w3.org
On Wed, 2007-02-21 at 20:14 +0100, Michael Schneider wrote: > As an example, I would say that OWL-DL is /more expressive/ than > OWL-Lite, because the set of OWL-DL ontologies is a real superset of the > set of all OWL-Lite ontologies, where I regard an ontology as a set of > syntactically wellformed OWL-axioms. For instance, you can have an > OWL-DL ontology containing an axiom like > > Class(C equivalentClass(complementOf(D)) > > but such an ontology would not be allowed in OWL-Lite. So, by "more > expressive" I mean that there are more syntactical expressions possible. Who uses "expressive" with this meaning? Certainly not the annual EXPRESS series of conferences on expressiveness in concurrency, the 14th of which will be in Lisbon in September. For them, just because language L has two syntactically different ways of expressing a concept that L' has only one expression for doesn't make L more expressive than L'. On the other hand if you make expressiveness a semantic notion then you run into the problem of the semantics for "complementOf(D)". For D = "registered Democrats," are Santa's elves and the states of bliss in complementOf(D)? How do OWL-DL users typically use complementOf, and what do they think it means? Relative complement is not so problematic, e.g. dogs that aren't Dalmatians, or voters that aren't registered Democrats. It's also ok to have dogs that aren't registered Democrats or voters that aren't Dalmatians provided the ontology admits the intersection of dogs and voters as a class (a competent type-checking ontology might object to this class on the ground that dogs don't vote, as a way of catching more errors). Absolute complement however seems neither terribly useful nor terribly tractable from either a theory or implementation standpoint, and so doesn't seem like a strong selling point for OWL-DL over OWL-Lite. Vaughan Pratt
Received on Thursday, 22 February 2007 18:10:56 UTC