[xacml-comment] Comment on condition element

A rule may hold both a target and a condition, but

631 The <Target> element may be absent from a <Rule>.  In this case, the
<Rule> inherits its target
632  from the parent <Policy> element.

A policy may hold a target but is not permitted to hold a condition.

Why is a condition not permitted at the policy (or policy set) level?

If a policy target is intended to server the function of a rule target in
the absence of a target in the rule then why can a policy level condition
not also be allowed?

An example where this would be useful is if policy objects are identified
with roles. In this context there is an over-arching policy-wide reqirement
that the subject be a member of the associated role. This would probably
need to be described as a condition - and most conveniently as a policy
level condition. However this is not possible in the current specification.

Thanks

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David Sutton
Software Architect
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