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[protege-owl] Restriction of instances in OWL?

Thomas Russ tar at ISI.EDU
Mon May 26 21:16:18 PDT 2008

On May 23, 2008, at 8:49 AM, Frank Puhlmann wrote:
> Now I would like to define a Class "SmallDepartment" that contains  
> all individuals of the class Department that have a maximum of three  
> individuals of Person working in the Department.
> Informally, something like this:
> Class SmallDeparment
> definedBy: each ?department with Number_of_individuals(?person) < 4
> with ?person as the set of individuals working in ?department (via  
> the hasRole/hasDepartment links)
> Can this be expressed in OWL?

Yes, this is easy to do using a max cardinality restriction.

You would just attach that restriction to the appropriate property.

Now, it turns out that this will generally not help you in inferring  
that a particular department is a small department because open world  
reasoning makes it hard to evaluate maximum cardinality restrictions.   
That is because unless you create additional assertions to close the  
set of potential fillers, an OWL reasoner cannot know that there  
aren't some other, not yet known fillers, and thus it can't compute  
maximum cardinality by counting fillers.  Note also that counting  
fillers requires allDifferent assertions as well, since OWL doesn't  
use a unique name assumption either.

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