Types, or: Where's the Difference Between CCS and pi?

  • Authors:

  • Davide Sangiorgi

  • Affiliations:

  • -

  • Venue:
  • CONCUR '02 Proceedings of the 13th International Conference on Concurrency Theory
  • Year:
  • 2002

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Abstract

The 驴-calculus is the paradigmatic calculus of mobile processes. With respect to previous formalisms for concurrency, most notably CCS, the most novel aspect of 驴-calculus is probably its rich theory of types. We explain the importance of types in the 驴-calculus on a concrete example: the termination property.A process M terminates if it cannot produce an infinite sequence of reductions M 驴驴 M1 驴驴 M2. . .. Termination is a useful property in concurrency. For instance, a terminating applet, when loaded on a machine, will not run for ever, possibly absorbing all computing resources (a 'denial of service' attack). Similarly, termination guarantees that queries to a given service originate only finite computations.We consider the problem of proving termination of non-trivial subsets of CCS and 驴-calculus. In CCS the proof is purely combinatorial, and is very simple. In the 驴-calculus, by contrast, combinatorial proofs appear to be very hard.We show how to solve the problem by taking into account type information.