12. The system of claim 11 , wherein the PEP further comprises: policy decision means for partially evaluating an attribute-based AC policy by evaluating the AC policy for a partial policy decision request constructed on the basis of attribute values provided by the attribute evaluating means, whereby a simplified attribute-based AC policy is obtained; and analysing means for deriving an access condition, for which a simplified AC policy provided by the policy decision means evaluates to permit access.
13. The system of claim 12 , wherein the analysing means of the PEP is adapted to: rewrite a simplified policy by substituting one or more auxiliary attributes for a Boolean-valued condition (BDD); convert at least part of the rewritten policy into a binary decision diagram; analyse said binary decision diagram with respect to satisfiability in order to determine a satisfiability condition in terms of one or more auxiliary attributes, wherein all paths in the binary decision diagram evaluating to either true or false are derived; and convert said satisfiability condition in terms of the one or more auxiliary attributes into an access condition in terms of one or more attributes in the simplified AC policy.