Multi-Message Exchange Examples

Hi,

I need to be able to do a multi-message exchange between the PDP and the PEP. Is there any example out there showing how this is done? I know that with the SAML profile for XACML you are able to do this and I know that this functionality already exists in XACML 2.0. It's just that examples work much better for me to understand this!

I need to query the context handler from a policy for an attribute based on the request. After getting the attribute from the context handler, I need to use that attribute value in an attribute selector to pull some information out of the resource content. I want to know if this is possible?

Thanks in advance,
Michael