Re: A Problem With The Semantics of DAML+OIL Restrictions

Tim Berners-Lee:
>Having just caught up on this thread I feel the basic diconnect is in
>the question, "How do we know what is the sufficient condition to
>be a member of restriction R"?
>
>You never do know.  You are only given some *necessary* conditions.

Well, that doesn't seem to be the case in DAML+OIL, where the 
conditions *can* be stated to be necessary and sufficient. Obviously, 
there are cases where one wants to be able to say this, to be able to 
give necessary and sufficient conditions. We do this when we say two 
names are equivalent, for example, in effect. But I think your point 
arises in the form: how can we adopt this open-ended attitude, and 
state necessary conditions on restrictions *without* saying they are 
sufficient? That would be easy to characterise semantically, but I 
suspect might place a burden on a DAML+OIL reasoner which would break 
decideability.  (? Any DL expert care to comment?)

>You have to replace the question "is this consistent with the
>restriction R?" with "is this consistent with the document D?".
>
>As you point out, R is just an abstract thing, a class.  And
>anyone can say anything about anything, you don't know
>whether there are any other constraints on it.

Sure, but that's a different question. If you state N&S conditions on 
something and I also state N&S conditions on the same thing, then 
taken together we will have said that our N&S conditions are 
equivalent (even if we didnt intend to :-) . But that doesn't remove 
our freedom to state the conditions independently.

Pat

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Received on Monday, 23 July 2001 20:27:25 UTC