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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 108 (13 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.
The Update Calculus
, 1997
"... In the update calculus concurrent processes can perform update actions with side effects, and a scoping operator can be used to control the extent of the update. In this way it incorporates fundamental concepts both from imperative languages or concurrent constraints formalisms, and from functional ..."
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Cited by 72 (3 self)
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In the update calculus concurrent processes can perform update actions with side effects, and a scoping operator can be used to control the extent of the update. In this way it incorporates fundamental concepts both from imperative languages or concurrent constraints formalisms, and from functional formalisms such as the  and calculi. Structurally it is similar to but simpler than the calculus; it has only one binding operator and a symmetry between input and output. We define the structured operational semantics and the proper bisimulation equivalence and congruence, and give a complete axiomatization. The calculus turns out to be an asymmetric subcalculus. 1 Introduction Theory of concurrent computation is a diverse field where many different approaches have been proposed and no consensus has emerged on the best paradigms. In this paper we take a step towards unifying two seemingly contradictory schools of thought: global vs local effects of concurrent actions. We define a calc...
Localities and Failures
 In Proc. 14th Foundations of Software Technology and Theoretical Computer Science
, 1995
"... We present a simple extension of the ßcalculus with located actions and channels and with location names as firstclass data, which models the notion of locality and failure present in the higherorder, distributed programming language Facile. The interaction between localities and failures disting ..."
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Cited by 56 (0 self)
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We present a simple extension of the ßcalculus with located actions and channels and with location names as firstclass data, which models the notion of locality and failure present in the higherorder, distributed programming language Facile. The interaction between localities and failures distinguishes our approach from previous ones where the notion of locality is considered in isolation. We argue that the combination of these two features leads, at least from the distributed programming viewpoint, to a more natural semantics. We then discuss the translation of this calculus into a standard simplysorted ßcalculus and show its adequacy with respect to a barbed bisimulation based semantics. In the translation each location is represented by a special process which interacts, by means of a simple protocol, with any process of the original program that wants to access resources depending on that location. We also employ our translation in the verification of a very simple faulttoler...
Bisimulations in the joincalculus
 Theoretical Computer Science
, 1998
"... We propose an objectoriented calculus with internal concurrency and classbased inheritance that is built upon the join calculus. Method calls, locks, and states are handled in a uniform manner, using asynchronous messages. Classes are partial message definitions that can be combined and transforme ..."
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Cited by 50 (6 self)
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We propose an objectoriented calculus with internal concurrency and classbased inheritance that is built upon the join calculus. Method calls, locks, and states are handled in a uniform manner, using asynchronous messages. Classes are partial message definitions that can be combined and transformed. We design operators for behavioral and synchronization inheritance. We also give a type system that statically enforces basic safety properties. Our model is compatible with the JoCaml implementation
Constraints as Processes
 Proceedings of CONCUR '96, volume 1119 of LNCS
, 1996
"... We present a compositional encoding of the flcalculus into the calculus. The former, used in the Oz semantics, is a recent small language with equational constraints over logical variables; the latter is a basic calculus of interacting processes. We establish a close correspondence between the ..."
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Cited by 9 (2 self)
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We present a compositional encoding of the flcalculus into the calculus. The former, used in the Oz semantics, is a recent small language with equational constraints over logical variables; the latter is a basic calculus of interacting processes. We establish a close correspondence between the reductions in the flcalculus and its encoding, using weak barbed bisimulation congruence. 1 Introduction In this paper we shall relate two different strands in the semantics of programming languages. One is the concurrent constraints paradigm where facts about data values combine to resolve goals; the other is the communicating processes paradigm where parallel agents interact through data transmission. We shall use two small semantic calculi which embody these paradigms in a rigorous and tractable format: the flcalculus for concurrent constraints and the calculus for communicating processes. These calculi have been deemed successful as semantic bases for programming languages in thei...
A Mechanized Theory of the picalculus in HOL
, 1992
"... : The ßcalculus is a process algebra for modelling concurrent systems in which the pattern of communication between processes may change over time. This paper describes the results of preliminary work on a definitional formal theory of the ßcalculus in higher order logic using the HOL theorem prov ..."
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Cited by 8 (0 self)
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: The ßcalculus is a process algebra for modelling concurrent systems in which the pattern of communication between processes may change over time. This paper describes the results of preliminary work on a definitional formal theory of the ßcalculus in higher order logic using the HOL theorem prover. The ultimate goal of this work is to provide practical mechanized support for reasoning with the ßcalculus about applications. Introduction The ßcalculus [17, 18] is a process algebra proposed by Milner, Parrow and Walker for modelling concurrent systems in which the pattern of interconnection between processes may change over time. This paper describes work on a mechanized formal theory of the ßcalculus in higher order logic using the HOL theorem prover [8]. The main aim of this work is to construct a practical and sound theoremproving tool to support reasoning about applications using the ßcalculus, as well as metatheoretic reasoning about the ßcalculus itself. Four general prin...
A Framework for Querying in Business Process Modelling
"... Abstract: In order to respond quickly to changing market requirements, a business organisation needs to increase the level of agility in all phases of the business process engineering chain. Business process (BP) modelling is the first and most important phase in this chain. Designing a new and rede ..."
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Cited by 4 (1 self)
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Abstract: In order to respond quickly to changing market requirements, a business organisation needs to increase the level of agility in all phases of the business process engineering chain. Business process (BP) modelling is the first and most important phase in this chain. Designing a new and redesigning an existing process model is a highly complex, time consuming and error prone task. In this work, we contribute to BP modelling by designing and implementing a framework for querying in business process modelling which i) supports decision making, ii) facilitates reuse of modelling artefacts and iii) helps ensuring compliance of models to relevant regulations. 1
Spi Calculus Translated to πCalculus Preserving May Testing
, 2003
"... We present a concise and natural encoding of the spicalculus into the more basic πcalculus and establish its correctness with respect to a formal notion of testing. This is particularly relevant for security protocols modelled in spi since the tests can be viewed as adversaries. The translation has ..."
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Cited by 4 (0 self)
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We present a concise and natural encoding of the spicalculus into the more basic πcalculus and establish its correctness with respect to a formal notion of testing. This is particularly relevant for security protocols modelled in spi since the tests can be viewed as adversaries. The translation has been implemented in a prototype tool. As a consequence, protocols can be described in the spi calculus and analysed with the emerging flora of tools already available for π. The translation also entails a more detailed operational understanding of spi since high level constructs like encryption are encoded in a well known lower level. The formal correctness proof is nontrivial and interesting in its own; so called context bisimulations and new techniques for compositionality make the proof simpler and more concise. 1
On the Benefits of Using the UpTo Techniques for Bisimulation Verification
"... We advocate the use of the up to techniques for bisimulation in the field of automatic verification. To this end, we develop a tool to perform proofs using the up to structural congruence, the up to restrictions and the up to parallel composition proof techniques for bisimulation between calculus te ..."
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Cited by 3 (0 self)
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We advocate the use of the up to techniques for bisimulation in the field of automatic verification. To this end, we develop a tool to perform proofs using the up to structural congruence, the up to restrictions and the up to parallel composition proof techniques for bisimulation between calculus terms. The latter technique is of particular interest because it allows one to reason on infinite state space processes. To use it in full effect, we adapt the on the fly bisimulation checking algorithm, leading to a form of computational completeness. The usefulness of these techniques in dealing with the expressive power of the calculus is illustrated on two non trivial examples, namely the treatment of persistent data structures and the alternating bit protocol. These examples are also good opportunities to study how well known calculus encodings behave in the framework of automatic verification.