Re: Cardinality in the open world

<snip/>

> 
> Well, as I've said, I wasn't accepting the idea of an unsatisfiable
> condition.  Now that I do, it changes things a little.
> 
> However, what I've come to is a situation where minCardinality either
> leads to an unsatisfiable condition, or else it is always satisfiable. 
> Finding instances of an unsatisfiable class is easy to do.  However, if
> the minimum cardinality is satisfiable, then the system will always be
> consistent.  Does this restriction provide any useful information in
> this case?  It would seem not.

IMO, minimum cardinality can be useful with the right expectations and
when used properly. You do not use minimum cardinality to check your
data with respect to the restriction (which is what you usually do with
database constraints), but you use minimum cardinality to infer
additional information (ok, this is a slight misuse of terminology, but
it makes sense intuitively IMHO).

Take, for examples, the following OWL knowledge base (in abstract syntax):

Class(Person partial restriction(hasFather minCardinality(1)))

Individual(john type(Person))


You might want to query whether john has a father, i.e., whether there
is a value for the property hasFather. Your query will return "yes".


What you seem to want to do is to check data you add to your knowledge
base with respect to closed-world constraints, i.e., constraints with
respect to the data in the knowledge base.
This is currently not possible in OWL, but I think this would be a very
useful extension.


Best, Jos

> 
> I find it ironic that my understanding has changed, but the consequences
> are still the same.  :-)
> 
> (OK, the consequences of a unsatisfiable class are now different, but
> the idea that using minCardinality to actually count anything is useless
> has not changed at all).
> 
> Regards,
> Paul Gearon
> 
> 
> 


-- 
Jos de Bruijn, http://homepage.uibk.ac.at/~c703239/
+43 512 507 6475
                              jos.debruijn@deri.org

Digital Enterprise Research Institute (DERI)
                               http://www.deri.org/

Received on Friday, 8 April 2005 09:08:47 UTC