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Hennicker, Rolf (2016): A Calculus for Open Ensembles and their Composition. In: Leveraging Applications of Formal Methods, Verification and Validation: Foundational Techniques. 7th International Symposium, ISoLA 2016, Imperial, Corfu, Greece, October 10–14, 2016, Proceedings, Part I. Lecture Notes in Computer Science, Vol. 9952. Cham: Springer. pp. 570-588
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We consider specifications of dynamically evolving ensembles consisting of entities which collaborate through message exchange. Each ensemble specification defines a set of messages, a set of process type declarations and an initial ensemble state. An ensemble state is given by a set of process instances that can trigger the creation of further process instances during ensemble evolution. We distinguish between internal and external messages of an ensemble. Internal messages are exchanged between the participants of a single ensemble while the external messages can be considered as ensemble interfaces which give rise to a composition operator for open ensemble specifications. A structural operational semantics for open ensemble specifications is provided based on two levels: a process and an ensemble level. We define an equivalence relation for ensemble specifications which generalizes bisimulation to dynamic architectures. As a main result we prove that equivalence of ensemble specifications is preserved by ensemble composition. We also introduce a semantic composition operator on the level of labeled transition systems and show that it is compatible with the syntactic composition of ensemble specifications;i.e. our semantics is compositional.