- From: Ian Horrocks <horrocks@cs.man.ac.uk>
- Date: Sun, 7 Apr 2002 13:02:45 +0100
- To: Dan Connolly <connolly@w3.org>
- Cc: David Martin <martin@ai.sri.com>, www-rdf-logic@w3.org
On March 29, Dan Connolly writes: > On Fri, 2002-03-15 at 16:01, Ian Horrocks wrote: > > On March 15, David Martin writes: > [...] > > > > I understand from the Pan and Horrocks paper at > > > > http://img.cs.man.ac.uk/jpan/Zhilin/download/Paper/Pan-Horrocks-rdfsfa-2001.pdf > > > > that there is a layering problem in the RDF/RDF(S) definition that > > > > prevents a clean division between successive metamodel levels. Is the > > > > relationship between rdfs:Class and daml:Class somehow connected to > > > > this? > > > > More or less. The extension of a DAML+OIL class should be a set of > > individuals (well, strictly a set of objects that are denoted by > > individual names) and not, say, a set of properties, as could be the > > case for an rdfs:Class. Because of the lack of layering in the rdf > > architecture there is no way to enforce this, so daml:Class is just a > > label given to the subset of rdfs:Classes that have the property we > > want. > > Ian, please be clear that this is your personal opinion of DAML+OIL, > not the consensus of the group that designed it. > > I don't want this property. > > I consider the design unfinished, as we agreed 20 Feb 2001: > > RESOLVED: We will release an updated language release > incorporating the current proposal, acknowledge the outstanding > issues and concerns, and solicit feedback from the larger > community. > > -- http://www.daml.org/committee/minutes/2001-02-20.html > > I'm quite disappointed that the concerns weren't actually > acknowledged in the spec that was released. > > Meanwhile, there are two different formalizations of DAML+OIL: > * model-theoretic-semantics.html - > revised Model-Theoretic Semantics > * axiomatic-semantics.html - revised Axiomatic Semantics > (from August 2001) > > http://www.daml.org/2001/03/daml+oil-index.html > > Note the axiomatic semantics doesn't have this bug involving separation > of datatypes from the rest of the universe of discourse. It isn't a bug, its a feature. Without the separation, the scope of the semantics needs to include all the XML Schema datatypes and built-in predicates. I don't think we want to go there (and I am sure that the axiomatic semantics doesn't do so). Ian > > > Note that in the daml+oil-ex.daml file, daml:Class is used > > extensively. Also note that many of the "meta" properties in the daml > > language definition have daml:Class as a range/domain so that classes > > used in daml ontology will often be implicitly of type daml:Class. > > > > > > > > > > I suppose all I'm really asking is: when would I use rdfs:Class and when > > > > would I use daml:Class? And if it doesn't matter, why are there two of > > > > them? > > > > Always use daml:Class. > > Or never use it. I don't think it's useful. > > > I hope I explained why there are two. > > -- > Dan Connolly, W3C http://www.w3.org/People/Connolly/ >
Received on Sunday, 7 April 2002 08:05:14 UTC