Architectural design support for composition and superimposition

The ever growing size and complexity of software systems is making it increasingly harder to build systems that meet both current and future requirements. During architecture design, many important design decisions are made. In this paper we present an architecture design notation based on UML activity diagrams. The notation allows for the specification of architecture fragments and supports composition of these fragments as well as their superimposition on each other. This notation allows us to make various compositions of architecture fragments (reflecting design decision alternatives) to adapt the architecture to new requirements. We have found that our notation is very suitable for modelling separate concerns at the architectural level.