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[protege-owl] Closed world/Open world

James A Miller James_A_Miller at raytheon.com
Mon Oct 6 11:48:40 PDT 2008


Timothy, Tom,

Thanks for your answers.  They are very helpful.

Jim 





Thomas Russ <tar at ISI.EDU> 
Sent by: protege-owl-bounces at mailman.stanford.edu
10/06/2008 02:28 PM
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Re: [protege-owl] Closed world/Open world







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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