On the Expressiveness of Coordination
Abstract
The expressiveness of communication primitives has been explored in a common framework based on the π-calculus by considering four features: synchronism (asynchronous vs synchronous), arity (monadic vs polyadic data), communication medium (shared dataspaces vs channel-based), and pattern-matching (binding to a name vs testing name equality vs intensionality). Here another dimension coordination is considered that accounts for the number of processes required for an interaction to occur. Coordination generalises binary languages such as π-calculus to consider languages that can performing joining that combines inputs such as the Join Calculus, splitting that combines outputs; full-coordination that supports both joining and splitting. By means of possi-bility/impossibility of encodings, this paper shows the following results. Coordination is orthogonal to other features and no combination of non-coordination features can encode joining, splitting or full-coordination into a binary language. Joining and splitting can encode one another when the source language does not include name-matching or intensionality, and the target language can represent channel-based communication. Otherwise joining languages cannot encode splitting languages, and vice versa. Full-coordination cannot be encoded into either joining or splitting.
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