We discuss the definition and modeling of reference of architectures, and the notion of conformance. NSA’s MISSI (Multilevel Information System Security Initiative) security reference architecture is used as an illustrative example. We demonstrate that an ADL should have not only the capability to specify interfaces, connections, and operational constraints, but also to specify how it is related (Or conforms) with other architectures or to implementations. A reference architecture such as MISSI is defined in Rapide [14] as a set of hierarchical interface connection architectures [17]. Each Rapide interface connection architecture serves as a reference architecture – an abstract architecture that allows a number of different implementations, but which enforces a common structure and communication rules. The hierarchical reference architecture defines the MISSI policies at different levels and identifies standard components, communication patterns and policies common to MISSI compliant networks of computer systems.