A Theory for Requirements Specification and Architecture Design of Multi-Functional Software Systems

We extend the Focus model [2] and its interface theory of distributed concurrent interactive systems and their structuring into components. Our goal is the scientific foundation for two methodologically essential, complementary and orthogonal concepts for the structuring of multi-functional systems in software and systems engineering. One addresses essentially requirements engineering and the specification of the comprehensive user functionality of multi-functional systems in terms of their functions, features and services. The other addresses mostly the design phase with its task to develop logical architectures formed by networks of interactive components that are specified by their interface behavior. The first concept is of major interest for the requirements engineer, the second for the software architect. We show that these concepts are complimentary, how they work and fit together as milestones in requirements engineering and systems architecture design.