Re: Asserting subclasses of open ranges or domains

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_Agent
> This 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@mondeca.com
> ----------------------------------------------------
> Mondeca
> 3, cité Nollez 75018 Paris France
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