On the realizability of collaborative services

This paper considers compositional specifications of services using UML 2 collaborations, activity and interaction diagrams, and addresses the realizability problem for such specifications: given a global specification, can we construct a set of communicating system components whose joint behavior is precisely the specified global behavior? We approach the problem by looking at how the sequencing of collaborations and local actions may be described using UML activity diagrams. We identify the realizability problems for each of the sequencing operators, such as strong and weak sequence, choice of alternatives, loops, and concurrency. The nature of these realizability problems and possible solutions are discussed. This brings a new look at already known problems: we show that given some conditions, certain problems can already be detected at an abstract level, without looking at the detailed interactions of the collaborations, provided that we know the components that initiate and terminate the different collaborations.