Re: beginner's question: Difference between CWA and NAF

CWA (Reiter, 1978), also called "negation as infinite failure", is a
mechanism that allow us to draw negative conclusions based on the lack of
positive information.
NAF (Clark, 1978), also called "negation as finite failure", is a weaker
notion of CWA in which "false" means FINITELY failed.

A very very stupid example is the following.

f(a).
f(b).
f(X) :- f(X).

"not f(c)" follows from CWA, but cannot be concluded by NAF (the SLD-tree is
infinite).

Please consider to search on the net... g**gle
Regards,
M


"DaMenge" <c-programming@xxxxxxxxxxxxxx> ha scritto nel messaggio
news:1124109030.630953.13870@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> with "NAF => CWA" ,I mean :
> "if one can suppose, that NAF leads to a correct interpretation of
> negation then one can conclude the assumptions made by CWA"
>
> Another way to say it : If you tell someone, who never heard anything
> about CWA and NAF, that he can get the value of "not q(X)" in
> p(X) :- s(X,Y), not q(X)
> by checking all positive substitutes given by that s-literal in q to be
> stored (or been proven in Prolog)
> ie: let a positive substitution given by s , say X=a
> if q(a) is proven(/stored), then "not q(a)" is wrong and if it's not,
> then "not q(a)" is true.
>
> With this rule of evaluation one should conclude the assumptions of the
> CWA.
>
> I guess i am wrong, but I don't see why at the moment.
>
> Perhaps someone could give me an exact definition (for both: CWA and
> NAF) first ?
>
> thx for your help !
>


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