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[protege-owl] Closed world/Open world

Thomas Russ tar at ISI.EDU
Mon Oct 6 11:27:31 PDT 2008


On Oct 5, 2008, at 6:11 PM, James A Miller wrote:

>
> Hello everyone,
>
> This is a follow-up to a statement (from Thomas Russ)  in an earlier  
> post:
>
> "Well, that seems to rely on closed-world reasoning, which is also not
> supported in OWL."
>
> I have seen this statement for several years now, but I am curious-- 
> what is it about OWL in particular that would prevent a reasoner  
> from treating the given ontology and data in a closed-world  
> fashion?  I don't understand how OWL itself enforces open world  
> reasoning; it seems that a reasoner could implement a mode that  
> treats the data as complete (closed).  Why is this not possible?

It is certainly possible to write reasoners like that.

Other description logics(*) have had reasoners that support closed  
world assumptions.  But that does take you into a different semantic  
arena (as Timothy Redmond indicates).  One aspect is that closed world  
is generally treated as an ASSUMPTION rather than a hard fact, so you  
have to introduce a notion of defeasability into the language.  It  
also requires that you have semantics for non-monotonic reasoning,  
since adding new information can cause previous conclusions to have to  
be revised.

For example, if you had the following classes:

    2-door-car <=>  car and exactly 2 has-door
    4-door-car <=>  car and exactly 4 has-door

and then asserted

    car-1 has-door door-1
    car-2 has-door door-2

you could satisfy 2-door-car.  Adding additional assertions

    car-1 has-door door-3
    car-1 has-door door-4

would require retracting the previous type classification (2-door-car)  
and adding 4-door-car in its place.  (Assuming, of course that all of  
the doors are different from each other).

-Tom Russ

(*) Loom http://www.isi.edu/isd/LOOM is one such system that I have  
been involved in the development of.  It has closed-world and other  
practical reasoning strategies, but lacks the clearly articulated  
semantics of OWL.




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