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RE: car color defaults: a story about Scoped Negation As Failure/log:notIncludes

From: Gerd Wagner <wagnerg@tu-cottbus.de>
Date: Thu, 7 Jul 2005 23:26:20 +0200
To: "'Michael Kifer'" <kifer@cs.sunysb.edu>, "'Dan Connolly'" <connolly@w3.org>
Cc: <public-rule-workshop-discuss@w3.org>
Message-Id: <20050707212714.99C7450810F@smtp2.TU-Cottbus.De>

> In fact, every use of default negation *always* had a clear 
> scope and I am not aware of anyone who (thoughtfully) advocated 
> default negation and imagined otherwise.

I guess Dan and others are concerned about making the
scope explicit in the object language. This is indeed
an option that is not supported by traditional formal
LP languages (although it is supported by Prolog's
metaprogramming capabilities). But you (Michael) say 
that FLORA-2 supports making the scope explicit, right? 
Maybe you can give us an example how this looks like 
in FLORA-2 and what it means in the underlying formal
semantics? 

> Finally, I would like to say once again that the term 
> "negation as failure" is bad and misleading. 
> Traditionally, negation as failure meant the
> particular strategy used in Prolog. NAF is just one 
> of the known forms of default negation.

Why should the term "default negation" be better and 
less misleading than the term "negation as failure"?
I think the latter says more about the meaning of NAF
than the former.

-Gerd
Received on Thursday, 7 July 2005 21:27:21 GMT

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