On the expressiveness of interaction

Subbisimilarity is proposed as a general tool to classify the relative expressive power of process calculi. The expressiveness of several variants of CCS is compared in terms of the subbisimilarity relationship. Similar investigation is also carried out for the variants of the pi calculus. The relative expressiveness of the different forms of the choice operation and the different ways of introducing infinite behaviors are systematically studied in both the frameworks of CCS and pi. Some issues concerning the expressiveness of both CCS and pi are clarified. Several open problems are solved along the way. The subbisimilarity approach and the relative expressiveness results are applied to show the independence of the operators of the pi calculus. The definition of the subbisimilarity relationship can be further strengthened with computational requirement, leading to a uniform treatment of computation and interaction.