On Sep 9, 2009, at 9:00 AM, Bernard Vatant wrote: Thanks Pat to jump in this
My pleasure:-) But I will be off-email again for a few more days after this post. Back next week.
We could as well define a tautological class dcterms:Topic as the range of dcterms:Subject, and assert only subclasses.
Is that clearer?
What is not clear is why you want to do this. Even in the case of the domestic appliances, if you do not put any necessary conditions on this class, you have effectively said nothing.
OK. I'm certainly dumb, but in what is this different, say, from the definition of the class foaf:Agent at http://xmlns.com/foaf/spec/#term_AgentThis class has no superclass, hence no necessary condition. Right?
Right, and indeed, speaking now strictly formally, the FOAF ontology hardly says anything about its classes. Almost all the useful content is in the English glosses. Which is fine, let me emphasize, but you were the one who thinks that for your example, this isn't enough :-)
It has two declared subclasses foaf:Person and foaf:Organisation. Those provide sufficient conditions, hence nothing if I understand well.
foaf:Agent the domain and range of some properties, but this again provides also sufficient conditions. Right?
Would you say that foaf:Agent is not defined and even useless, since it has no necessary condition?
I'd say (and in fact often do say) that FOAF is a good example of a useful ontology which is almost nonexistent as a formal specification, and gets all its meaning from the way its terms are actually used. It is a socially defined ontology rather than a logically defined one. Another example is dublin core. The primary use of the formal axioms in cases like this is to be a guide for users in how to apply the vocabulary to instance data, rather than to support complex inferences.
Just my own 2c, of course, and Im sure others will disagree.
Pat
The same for many top classes in many ontologies. No?
Thanks for clarifying this.
It is tricky to appeal to intuition in cases like this, because of course we all know that there are things that are not domestic appliances, and we tend to use this knowledge without being told that we have to. But our ontologies only know stuff like this if we somehow tell them it explicitly.
Indeed. Nobody argues on that :))
Bernard
--
Bernard Vatant
Senior Consultant
Vocabulary & Data Engineering
Tel: +33 (0) 971 488 459
Mail: bernard.vatant@xxxxxxxxxxx
----------------------------------------------------
Mondeca
3, cité Nollez 75018 Paris France
Web: http://www.mondeca.com
Blog: http://mondeca.wordpress.com
----------------------------------------------------
------------------------------------------------------------ IHMC (850)434 8903 or (650)494 3973 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32502 (850)291 0667 mobile
|