Modeling Architectural Non Functional Requirements: From Use Case to Control Case

While the functional requirements of a system can be effectively modeled through the use case driven approach, there is no standard or de facto method for modeling non-functional requirements of the system architecture. Often such requirements are dealt with in a reactive manner rather than proactively. Yet increasingly a contributing factor in project difficulty and failure are the non-functional requirements imposed on the solution architecture. This paper proposes a control case approach to record and model non-functional requirements. This technique enables the control case to represent the nonfunctional requirements from different perspectives, most typically the various operating conditions. Furthermore, we propose an extension to the "4+1" view model for depicting software architecture by adding the control case view. The combination of both the use case and control case views thus reflects the complete requirements across the collective system life cycle views: design, process, implementation and deployment