Hierarchical resource profile of XACML v2.0

Hi Guys,

Reading the Hierarchical resource profile of XACML v2.0, I am a little 
puzzled by "3.1 Nodes in an XML document" requiring that not only should 
one include a resource-id of type xpath-expression for the node that is 
the resource for the access decision but also it parent and all 
ancestors. Why is this required by the spec? Why is it necessary. Should 
an impl of a PDP not simply be able to traverse the parent and ancestors 
of the node using normal XML processing and node traversal mechanism in 
teh various xml processing tools and apis?

I must be missing something obvious. Thanks for any explanation.

-- 
Regards,
Farrukh

Web: http://www.wellfleetsoftware.com