W3C home > Mailing lists > Public > public-rif-wg@w3.org > January 2007

Re: slotted notation -summary

From: Chris Welty <cawelty@gmail.com>
Date: Fri, 05 Jan 2007 19:16:28 -0500
Message-ID: <459EEA5C.3090807@gmail.com>
To: Michael Kifer <kifer@cs.sunysb.edu>
CC: Dave Reynolds <der@hplb.hpl.hp.com>, RIF <public-rif-wg@w3.org>

Michael Kifer wrote:
> Chris Welty <cawelty@gmail.com> wrote:
>> However, and here is the crucial point, if I create a (direct) 
>> instance of Q, it will only have slot s1 and, in fact, CANNOT have 
>> slot s2.  In most of these systems you cannot "add slots" to an 
>> object.  In a real sense, the class you use to create an object has a 
>> very important impact on its existence.  So that a more faithful FOL 
>> rendering would be the three axioms above plus:
>> (forall (x) (if (and (Q x) (not (P x)))
>>                  (not (exists (y) (s2 x y)))))
>> (instances of Q don't have slot s2 unless they are instances of P)
>> But this is a translation nightmare - akin to accounting for negation 
>> as failure in FOL, but not quite the same.
> But I don't understand why do we need to worry about it.

Aha.  Yes, well, you've got me there.  I'm not sure we do.  But while 
we were on the topic of the difference between OO and RDF, I thought I 
would add this to the catalog.

> We don't need to have such an axiom in the core.
> In your favorite dialect, you decide if you want CWA (in which case the
> above behavior is ensured, but you can always add new knowledge and make x
> a member of P) or OWA. In the latter case, the above behavior cannot be
> simulated except at a very basic level (e.g., if P is specified
> extensionally rather than by rules).
> In either case, people can add whatever axioms they want to the dialect of
> their choice to make it mimic their favorite notion of a class.

We are on the same page.

Received on Saturday, 6 January 2007 00:16:46 UTC

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