Scientific Annals of Computer Science

"Alexandru Ioan Cuza" University of Iaşi

Contract-Oriented Computing in CO2

Published in, p. 5-60, doi: 10.7561/SACS.2012.1.5

Authors: M. Bartoletti, E. Tuosto, R. Zunino


We present CO2, a parametric calculus for contract-based computing in distributed systems. By abstracting from the actual contract language, our calculus generalises both the contracts-as-processes and contracts-as-formulae paradigms. The calculus features primitives for advertising contracts, for reaching agreements, and for querying the fulfilment of contracts. Coordination among participants happens via multi-party sessions, which are created once agreements are reached. We present two instances of our calculus, by modelling contracts as processes in a variant of CCS, and as formulae in a logic. We formally relate the two paradigms, through an encoding from contracts-as-formulae to contracts-as-processes which ensures that the promises deducible in the logical system are exactly those reachable by its encoding as a process. Finally, we present a coarse-grained taxonomy of possible misbehaviours in contract-oriented systems, and we illustrate them with the help of a variety of examples.

Keywords: contracts, concurrent constraint programming, multiparty sessions

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