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[protege-owl] Different levels of relations

Thomas Russ tar at isi.edu
Mon Nov 8 09:57:57 PST 2010


On Nov 7, 2010, at 5:09 AM, Paulo Urbano wrote:

> Regarding Thomas solution 4:
>
> 4.  You could dispense with the individuals entirely and work just  
> with the descriptions and the axioms describing the restrictions.   
> So, for example you could say
>
>   John type (some likes Music)
>   Frida type (some likes Rock)
>
> etc.  You could then use things like DL query to find individuals  
> that satisfy the restrictions that you want.  This can be a bit  
> cumbersome in that getting access to the details of the restrictions  
> isn't as easy as dealing directly with individuals and property  
> values, but it should be something you could reasonably encapsulate.
>
>
> Wouldn't the ontology be inconsistent as the existential restriction  
> would imply that John and Frida must have a value (individual) for  
> class Music and Rock respectively?

Why do you think this would make the ontology inconsistent?

Existential quantifiers do not require an actual individual filler  
because of open world semantics.

Now, one could debate whether there really is an individual of Music  
or Rock that the individual likes.  But perhaps the interpretation  
that you want is that the individual likes some songs that are  
Rock_Songs.  This is, of course, a relatively weak statement, since  
the SOME qualifier only requires one.  So there is a bit of a mismatch  
in the strict logical interpretation and the more common sense view of  
what it means to like Rock or Jazz.  But within the limitations of the  
OWL-DL language, you often have to make some accommodations to the  
expressive power and the need for crisp logical definitions of what  
are, in reality, more fuzzy notions.






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