I would second that. There is no need to standartize any attributes - XACML system may be used in cases where something we mandate will make no sense at all. Having an ID attribute for "subject" is not critical to anything - especially since we do not guarantee, or even suggest that it is unique. It is not harder to agree on the name of an attribute used for several interoperating systems, then to try to specify some scheme, of what this attribute are supposed to mean, for all systems using XACML. Daniel.