[xacml] Scope for hierarchical resource

Let me clarify my comments on hierarchical
resource.

>Tim: But what if document treated one way in policy,
but request

>   submitted other way.  resource identifier would identify
as a

>   single resource or as a structured document.

I am assuming that the semantics of the resource identifier
may vary from application to application. I think it is up to the contract
(agreement) between PEP and PDP and difficult to enforce syntactical restriction
on URI to distinguish single resource from a structured resource as a standard.
Please correct me if I am wrong.

For example, an access to a file is considered as
an access to a single resource. An access to one element in a XML document
is also considered as an access to a single resource. On the other hand,
access to an entire directory and an access to a subtree (i.e. elements
and attributes) in XML document is not considered as a single resource
access.

One way to tell XACML policy engine about this distinction
is to use scope attribute in the request. If the request specify decendant
as a scope, there needs some way to address target resource hierarchical
structure otherwise the engine cannot know the decendants.

Best,

Michiharu