The requirements specification and design specification of complex software systems has been a continual problem for the past three decades. This paper suggests an integrated approach for these two areas and provides the rationale on why this approach has been proposed for the Defense Information Infrastructure (DII) Common Operating Environment (COE). The DII is the most complex Department of Defense initiative undertaken to date. When fully implemented, it will operate as a collection of distributed heterogeneous information systems that will directly benefit the entire US Department of Defense. However, unlike other complex systems such as the "starwars" missile defence system of the past, most of individual components of the system are fairly well understood. In addition, the DII COE does not require software or hardware technology that does not currently exist. The challenge lies in the extensive scope of the system, and the level of integration and interoperability required.