question on "obligation"

Hi,

I am having difficulties in interpreting the spec regarding the application of the <obligation> element.

- May a PDP implementation call functions that are specified in the <obligation>? So could the <obligation> specify functions to be called *by the PDP* e.g. an external DataBase or e.g. a charging function.

- Another question that I have is - is it specified in the spec how to specify a certain sequence of policies/policy rules that are to be executed one after the other?

Thanks,

Paulus