Using a query XML element to match a resource within a Rule

Dear Colleagues,

I am currently working on the XACML Profile for the ebXML RegRep 4 
specifications.

In that profile, I would like to specify a way to somehow match a 
resource based on whether it matches a RegRep Query or not.
The query invocation is represented by an XML element defined by ebXML 
RegRep XML schema. Let us assume the following simplified
representation of this XML element:

<rim:Query/>

What is the best way to express this in an XACML2 Rule.

Thank you for your help.

-- 
Regards,
Farrukh Najmi

Web: http://www.wellfleetsoftware.com