The two dimensions of an architecture

A two-dimensional view on software architectures is introduced. One of the dimensions is the implementation-oriented view based on component structure, and the other is de ned by abstractions and logic of collaboration. We argue that unless the view based on collaboration is rigorously taken into account in early phases of the development, architectures will be based on informal expectations and implementation bias. This bias may then blur the logic of the speci cation, whereas an adequate use of abstractions of collaboration as basis for architecture will eliminate super uous di culties in design and veri cation.