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RE: NAF v. SNAF - where is this being addressed?

From: Gerd Wagner <wagnerg@tu-cottbus.de>
Date: Wed, 29 Jun 2005 22:23:29 +0200
To: "'Jim Hendler'" <hendler@cs.umd.edu>, <public-rule-workshop-discuss@w3.org>
Message-Id: <20050629202420.A55F250828E@smtp2.TU-Cottbus.De>

All, forgive me if I missed something since I wasn't able to attend the
workshop.  My understanding from the workshop report, and from discussion
with Tim BL and others afterwards, was that NAF wasn't going to make sense,
but SNAF would -- that is, on the Web, if there is not a mechanism for
defining the "KB" (graph) that a set of rules is applied to, there's not way
to use a geenralized negation as failure -- i.e. I cannot say to the "whole
web" that someone can be assumed to have two children unless it is shown
they have a different number.  Instead, I need a way to designate the
dataset that a rule like this is applied to.   
But isn't that the case with inferencing in general: it is scoped either
implicitly or explicity to some KB and never to the "whole Web" (whatever
that means)? For instance, if I use Racer with Protege/OWL, the scope is
implicitly the loaded ontology (including potential imports). Likewise, if I
use SWI Prolog, the scope is implicitly the loaded set of facts and rules.
So, it seems to me that there is some confusion about the meaning of "scope"
here. I think the real issue is to be able to express that if the attempt to
infer a statement (like some document being a W3C recommendation) from some
definitive KB (like the W3C site) fails, then we can infer that the
statement is false (and consequently its <neg>-negation, where <neg>
expresses falsity, holds). This means that for a predicate (class or
property), for which definitive knowledge is available, the failure to infer
a statement formed with it amounts to the falsity of that statement. For
other predicates failure does not amount to falsity. So we may employ a
negation for expressing failure (naf) and a negation for expressing falsity
(neg). In general, they are distinct, but in the case of definitive
knowledge they collapse.
This is not an issue of inferential scope, but of designating and using
definitive knowledge. Scope would be an orthogonal issue (it applies not
just to negation, but to inference in general).
Gerd Wagner
Email: G.Wagner@tu-cottbus.de
Brandenburg University of Technology
at Cottbus, Germany
Received on Wednesday, 29 June 2005 21:18:45 UTC

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