Deriving Bisimulation Congruences for Reactive Systems
The dynamics of reactive systems, e.g. CCS, has often been defined using a labelled transition system (LTS). More recently it has become natural in defining dynamics to use reaction rules - i.e. unlabelled transition rules - together with a structural congruence. But LTSs lead more naturally to behavioural equivalences. So one would like to derive from reaction rules a suitable LTS.
This paper shows how to derive an LTS for a wide range of reactive systems. A label for an agent a is defined to be any context F which intuitively is just large enough so that the agent Fa (“a in context F”) is able to perform a reaction. The key contribution of this paper is a precise definition of “just large enough”, in terms of the categorical notion of relative pushout (RPO), which ensures that bisimilarity is a congruence when sufficient RPOs exist. Two examples - a simplified form of action calculi and term-rewriting - are given, for which it is shown that sufficient RPOs indeed exist. The thrust of this paper is, therefore, towards a general method for achieving useful behavioural congruence relations.
KeywordsLabel Transition System Reaction Rule Process Calculus Term Context Structural Congruence
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