[xacml] New issue#1 from "Boolean Policy resolution"

PM-1-?: how NOT-APPLICABLE impacts a combinator expression  A  combinator expression  is a combination of predicates, where possible combinators are <AND>, <OR>, <NOT>, <N-OF>, <ORDERED-[AND OR N-OF]>.  This list of Combinators can be extended.  Example:  <AND>
predicate1,
predicate2,
predicate3 </AND>  The issue occurs when one or more of the predicates in the list returns a result of NOT-APPLICABLE (this can occur if the predicate is a <referencedPolicy>).  What should the result of the combinator expression be?  What if ALL predicates in the bominator expression return NOT-APPLICABLE?  Potential Resolution:  a) Any predicate evaluating to NOT-APPLICABLE is logically
removed from the combinator expression.
Example: if predicate3 in the example above returned a result of
NOT-APPLICABLE, then the combinator expression is the result of
<AND>
predicate1,
predicate2
<AND>  b) An empty combinator expression has the following results:
<AND></AND>
-> TRUE
<OR></OR>
-> FALSE
<NOT></NOT>
-> TRUE
<N-OF></N-OF> -> FALSE
<ORDERED-[whatever]> has same result as [whatever] above.
Extended combinators must define the result of an empty
expression.
Example: If predicates 1, 2, and 3 in the example above all
evaluate to NOT-APPLICABLE, then the combinator expression is
<AND></AND>, and the result is TRUE.  b)-alternative: An empty combinator expression has a result of
NOT-APPLICABLE.  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