Re: Cardinality in the open world

Peter Crowther wrote:
>>From: Jos de Bruijn [mailto:jos.debruijn@deri.org] 
>>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
> 
> 
> It's possible, but you sometimes need a few helper classes.  I've dealt
> with such checking in the past by constructing classes whose instances I
> know would be invalid, and then iterating through the instances of those
> classes.  For example, if I know that all OWL developers must have at
> least 3 heads [in order to understand the spec], I construct the class
> of OWL developers who have at most two heads and look for instances of
> that class.  Those instances fail my checks.

I am not really sure whether your class definition for OWL developers
with at most two heads would really work. Could you give me an example?

In any case, you use a procedure outside of OWL to circumvent the lack
of closed-world constraints.
You essentially query an OWL knowledge base and then apply closed-world
reasoning to the query result. Use of this reasoning procedure cannot be
 expressed in OWL. Furthermore, you cannot express the intention to use
the newly constructed class for contraint checking on the class of OWL
developers.
Actually, if you want to check the number of values for a certain
property, it would be easier to simply query for all values for the
property and then count the number of results of your query.


Best, Jos

> 
> 		- Peter
> 


-- 
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 10:37:49 UTC