Relying Party Defined Namespace Constraints (RPDNC) are limitations on the subject namespace issued by X.509 
certification authorities (CAs) that are defined and enforced by the end-point at the relying party side. As grid 
authentication based on X.509 credentials provides the subject DN as a handle that identifies the authenticated entity, 
the capability to ensure subject name uniqueness is of critical importance in ensuring overall integrity of the 
authentication system. 

This document described the rationale and use cases for relying party defined name space constraints, and lists the set 
of desired features a policy language expressing such constraints should have.