Specification of attribute relations for access control policies and constraints using Policy Machine

Attribute relations in access control mechanisms or languages allow accurate and efficient specification of some popular access control models. However, most of the access control systems including today´s de-facto access control protocol and specification language, XACML, does not provide sufficient syntactic and semantic support for the specification of attribute relations in their scheme. In this paper, we show the deficiencies of XACML in specifying such capabilities in the implementations of the Multilevel Security, Hierarchical Role Based policies and Separation of Duty requirements of access control systems. In comparison, we then demonstrate the attribute relation mechanism provided by a relation-based access control mechanism - the Policy Machine.