Re: [xacml] New issue#2 from "Boolean Policy resolution"

If the semantics of N-OF is "at least n of" why don't we call it that to
avoid confusion.

<AT-LEAST-N-OF n=[something greater than 0]>
</AT-LEAST-N-OF>

Also, I don't see why if N predicates do not exist than it is supposed to
be an error and not just FALSE.

If we take the semantics that a NOT-APPLICABLE is not counted then the
evaluation says that it must be false.

(N-OF(n=1) N) = (N-OF(n=1) ) = FALSE

I can see the value in helping a policy writer (should one human choose to
write XML) in that there is no hope for his expression to be true, but it
shouldn't be an error per say.

For example, if you take that approach of "pre-evaluating" expressions
then you should make such expressions as

<Equals>

<String>Polar</string>

<String>Anne</string>

<Equals>

should return an error at compliation/syntax checking as well.

Can we just say that if n is strictly greater than the predicates involved
then the expression will evaluate to FALSE. This approach works better
inductively, since we can make arguments for evaluation to be

(N-OF(n) x1,...,xm) =

(N-OF(n-1) x2,..,xm), if x1 = T

(N-OF(n) x1,...,xm),  if x1 = F

(N-OF(n) x1,...,xm),  if x1 = N (NOT-APPLICABLE)

E,
if x1 = E

So the following would be consistent with that evaluation strategy:

(N-OF(0) x1,...,xm) = T, even if m=0
(N-OF(n) )
= T, if n=0

= F, otherwise

A consequence of this is that
1. For all n>m, (N-OF(n) x1,...,xm) = F, and
2. N-OF never evaluates to NOT-APPLICABLE

Cheers,
-Polar

On Thu, 7 Feb 2002, Anne Anderson wrote:

>
> PM-1-?: result of <N-OF n=0> combinator expression
>
> We all agreed that <N-OF n=[something greater than 0]> was an
> error if there were not at least n predicates to be evaluated.
> We also agreed that the semantics of <N-OF> were "at least n
> of".  We did not agree on what should be the result of <N-OF
> n=0>.
>
> Potential Resolution:
>
> <N-OF n=0> results in TRUE, regardless of the results of the
> predicates in the combinator expression.
>
> Champion: Anne
>
> --
> Anne H. Anderson
Email: 
> Sun Microsystems Laboratories
> 1 Network Drive,UBUR02-311
Tel: 781/442-0928
>
Burlington, MA 01803-0902 USA
Fax: 781/442-1692
>
>

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