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[protege-owl] Checking inconsistence of a "some" relation

Thomas Russ tar at ISI.EDU
Sun Aug 5 22:03:14 PDT 2007


On Aug 3, 2007, at 9:32 PM, João Olavo Baião de Vasconcelos wrote:

> On 8/3/07, Samson Tu <swt at stanford.edu> wrote:
> However, the 'red border' check is a legacy from Protege frame. It  
> doesn't really  mean much in OWL, with its open world assumption.
>
> The fact that you don't have an explicit B instance associated with  
> A doesn't mean that the ontology is inconsistent.
>
> I got it. The open world assumption means that you can't assume  
> that a C isn't a B just bec they are distinct classes, right?
>
> But it's important to me to check if a C is/isn't a B for the sake  
> of consistence.

There are two different ways in which the open world assumption makes  
this difficult, if not impossible to verify.

Firstly, unless B and C are disjoint, then the B instance could also  
be a C.
This can be fixed by either making the classes B and C disjoint  
(assuming they are in fact meant to be disjoint), or by explicitly  
expressing the fact that the particular instance of B is not also a C.

Secondly, there is the possibility of some other instance of C that  
is a property value, but which is a different individual than the  
instance of B.  This one is harder to get around, since the some  
restriction only requires a single filler of that type.  It leaves  
open the possibility of other fillers of other types.

> What is the best way to check it? By swrl rules?

Short of imposing careful restrictions on the cardinality of the slot  
fillers and careful attention to disjointness, there isn't a lot you  
can do.  You can use queries to check for known consistency, but to  
find inconsistency requires that there be a proof that the  
inconsistency MUST happen.  That is really hard for negated  
propositions.  It's usually harder to prove negatives, since they  
involve universal statements rather than just finding an existing  
positive example.





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