AW: Asserting subclasses of open ranges or domains

Dear Bernard,

I took quite a while to think about those things.
What extra information is provided by explicitly allowing something? Consider the two statements "Books can be about every topic" and "Books can be about every topic and about dinosaurs" - aren't they equivalent? Or did I miss something here?

Yes, in the current stae of affairs, you're right, from a purely logical viewpoint, nothing is added by specifying subclasses of the range.  Let me take another example. Suppose you want to set an ontology of home appliances. You define a class "Home" and a property "hasAppliance".

Of course you can define the range of this property as "DomesticAppliance", but you don't give any necessary condition for this class, because you don't want to preclude any kind of stuff one can invent there. So this class has a quasi tautological definition, it is the range of "hasAppliance". No more, no less.

Now I can, not restrict this class, but say which kind of stuff is currently considered as domestic appliance. So I will define "WashingMachine", "HomeCinema", "BathTub" and whatever you like as subclasses of "DomesticAppliance". In short I have a list of sufficient conditions for this class, but no proper necessary conditions, beyond the tautological fact of being the value of "hasAppliance". Sure enough, if the ontology had been set a century ago, new subclasses would have emerge since, and an ontology set today does not want to preclude whatever the 21st century will bring about in this domain.

I don't think that such sufficient conditions are very useful, because in terms of logic, they do not change anything (if I remember right, one of your initial points was why they are discarded by some ontology editors, this is probably the reason: to a reasoner, they are redundant). Instead, I'd tackle things the other way around: leave the range unrestricted, and let people fill in whatever they want to. Then you can run a query to see what is commonly used as domestic appliance in the 21st century. Run that query again in the 22nd century (given that ontologies, reasoners and stuff are still up to date then...) and see how things have changed.

Best,
Heiko.