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The Fusion Calculus: Expressiveness and Symmetry in Mobile Processes (Extended Abstract)
 LICS'98
, 1998
"... We present the fusion calculus as a significant step towards a canonical calculus of concurrency. It simplifies and extends the πcalculus.
The fusion calculus contains the polyadic πcalculus as a proper subcalculus and thus inherits all its expressive power. The gain is that fusion contains action ..."
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Cited by 128 (14 self)
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We present the fusion calculus as a significant step towards a canonical calculus of concurrency. It simplifies and extends the πcalculus.
The fusion calculus contains the polyadic πcalculus as a proper subcalculus and thus inherits all its expressive power. The gain is that fusion contains actions akin to updating a shared state, and a scoping construct for bounding their effects. Therefore it is easier to represent computational models such as concurrent constraints formalisms. It is also easy to represent the so called strong reduction strategies in the lambdacalculus, involving reduction under abstraction. In the πcalculus these tasks require elaborate encodings.
The dramatic main point of this paper is that we achieve these improvements by simplifying the πcalculus rather than adding features to it. The fusion calculus has only one binding operator where the πcalculus has two (input and restriction). It has a complete symmetry between input and output actions where the πcalculus has not. There is only one sensible variety of bisimulation congruence where the picalculus has at least three (early, late and open). Proofs about the fusion calculus, for example in complete axiomatizations and full abstraction, therefore are shorter and clearer.
Our results on the fusion calculus in this paper are the following. We give a structured operational semantics in the traditional style. The novelty lies in a new kind of action, fusion actions for emulating updates of a shared state. We prove that the calculus contains the πcalculus as a subcalculus. We define and motivate the bisimulation equivalence and prove a simple characterization of its induced congruence, which is given two versions of a complete axiomatization for finite terms. The expressive power of the calculus is demonstrated by giving a straightforward encoding of the strong lazy lambdacalculus, which admits reduction under lambda abstraction.
Decoding Choice Encodings
, 1999
"... We study two encodings of the asynchronous #calculus with inputguarded choice into its choicefree fragment. One encoding is divergencefree, but refines the atomic commitment of choice into gradual commitment. The other preserves atomicity, but introduces divergence. The divergent encoding is ..."
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Cited by 103 (5 self)
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We study two encodings of the asynchronous #calculus with inputguarded choice into its choicefree fragment. One encoding is divergencefree, but refines the atomic commitment of choice into gradual commitment. The other preserves atomicity, but introduces divergence. The divergent encoding is fully abstract with respect to weak bisimulation, but the more natural divergencefree encoding is not. Instead, we show that it is fully abstract with respect to coupled simulation, a slightly coarserbut still coinductively definedequivalence that does not enforce bisimilarity of internal branching decisions. The correctness proofs for the two choice encodings introduce a novel proof technique exploiting the properties of explicit decodings from translations to source terms.
What's TyCO, After All?
, 2000
"... uniform TyCO ! a with at variants uniform TyCO \!" a with nested variants nonuniform TyCO !? > a with nested variants The setting TyCO is an namepassing process calculus featuring asynchronous communication between concurrent objects via labeled messages carrying names, prop ..."
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uniform TyCO ! a with at variants uniform TyCO \!" a with nested variants nonuniform TyCO !? > a with nested variants The setting TyCO is an namepassing process calculus featuring asynchronous communication between concurrent objects via labeled messages carrying names, proposed by Vasconcelos [Vas94]. In comparison to a standard calcu lus [MPW92], TyCOprocesses are indeed more like objects in the sense that every communication exchanges a structured value, reminiscent of method invocation, consisting of a name tagged with a label. More recently, Sangiorgi conceived a calculus equipped with labeled values, called variants, which has been brought up as a suitable vehicle for the description, by means of encodings, of the semantics of typed higherlevel object calculi [San98]. The two calculi have several commonly dened operators like the inactive process 0, parallel composition P 1 jP 2 , and restriction (a) P . However, their constructs for communication...