- From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
- Date: Wed, 12 Dec 2001 10:50:30 -0500
- To: lobrst@mitre.org
- Cc: www-webont-wg@w3.org
Precisely. Systems like Protege have a meta-level in the same sense that RDF has. The way you create classes is to create instances of a metaclass. However, this is not a modifiable meta level. A modifiable meta level would have something like what rdfs:ConstraintProperty was supposed to do. That is, it would be possible to either 1/ change the way that existing class constructs worked or 2/ add fundamentally different class constructs by creating metaclasses. One (very hard) example would be to add defaults to a formalism without them. Another (simpler) example would be to add range constraints to a formalism without them. There have been a number of proposals for this sort of meta level, going back to the 1970s. However, I'm not aware of any (continuing) use of these facilities, except in object extensions to LISP-like programming languages (e.g., CLOS). I should have ruled this out from the start. peter From: Leo Obrst <lobrst@mitre.org> Subject: Re: proposal for working on the ontology language Date: Tue, 11 Dec 2001 18:30:48 -0500 > Peter, > > Although not formalized, I am thinking of Protege (not that it's > modifiable, you can only add consistently defined new meta-classes). I > also think of CLOS, again as mostly an unformalized language. > > "Peter F. Patel-Schneider" wrote: > > > > From: Leo Obrst <lobrst@mitre.org> > > Subject: Re: proposal for working on the ontology language > > Date: Tue, 11 Dec 2001 18:14:42 -0500 > > > > [...] > > > > > I also note that there is no meta level to DAML+OIL and I think that was > > > a conscious choice, no?, though I don't know the history of that > > > decision. Sometimes having a modifiable meta level is a very good thing > > > (future language extensions, e.g.) > > > > > > Leo > > > > I would be very interested in hearing of cases where a modifiable meta > > level was actually used. I wouild be even more interested in hearing of > > such cases that also involved a logical formalism. > > > > peter > > -- > _____________________________________________ > Dr. Leo Obrst The MITRE Corporation > mailto:lobrst@mitre.org Intelligent Information Management/Exploitation > Voice: 703-883-6770 7515 Colshire Drive, M/S W640 > Fax: 703-883-1379 McLean, VA 22102-7508, USA
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