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34
A Calculus of Mobile Agents
, 1996
"... . We introduce a calculus for mobile agents and give its chemical semantics, with a precise definition for migration, failure, and failure detection. Various examples written in our calculus illustrate how to express remote executions, dynamic loading of remote resources and protocols with mobile ag ..."
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Cited by 271 (11 self)
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. We introduce a calculus for mobile agents and give its chemical semantics, with a precise definition for migration, failure, and failure detection. Various examples written in our calculus illustrate how to express remote executions, dynamic loading of remote resources and protocols with mobile agents. We give the encoding of our distributed calculus into the joincalculus. 1 Introduction It is not easy to match concurrency and distribution. Suppose, for instance, that we want to implement a concurrent calculus with CCSlike communication channels and with processes running on different physical sites. If we do not locate channels, we quickly face a global consensus problem for nearly every communication which uses the interconnection network. In a previous work [6], we introduced the joincalculus, an asynchronous variant of Milner's ßcalculus with better locality and better static scoping rules. It avoids global consensus and thus may be implemented in a realistic distributed en...
A Classification of Security Properties for Process Algebras
 JOURNAL OF COMPUTER SECURITY
, 1994
"... Several information flow security definitions, proposed in the literature, are generalized and adapted to the model of labelled transition systems. This very general model has been widely used as a semantic domain for many process algebras, e.g. CCS. As a byproduct, we provide a process algebra sim ..."
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Cited by 106 (16 self)
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Several information flow security definitions, proposed in the literature, are generalized and adapted to the model of labelled transition systems. This very general model has been widely used as a semantic domain for many process algebras, e.g. CCS. As a byproduct, we provide a process algebra similar to CCS with a set of security notions, hence relating these two areas of concurrency research. A classification of these generalized security definitions is presented, taking into account also the additional property of input totality, which can influence this taxonomy. We also show that some of these security properties are composable w.r.t. the operators of parallelism and action restriction.
Distributed Processes and Location Failures
 Theoretical Computer Science
, 1997
"... . Site failure is an essential aspect of distributed systems; nonetheless its effect on programming language semantics remains poorly understood. To model such systems, we define a process calculus in which processes are run at distributed locations. The language provides operators to kill locations ..."
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Cited by 56 (7 self)
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. Site failure is an essential aspect of distributed systems; nonetheless its effect on programming language semantics remains poorly understood. To model such systems, we define a process calculus in which processes are run at distributed locations. The language provides operators to kill locations, to test the status (dead or alive) of locations, and to spawn processes at remote locations. Using a variation of bisimulation, we provide alternative characterizations of strong and weak barbed congruence for this language, based on an operational semantics that uses configurations to record the status of locations. We then derive a second, symbolic characterization in which configurations are replaced by logical formulae. In the strong case the formulae come from a standard propositional logic, while in the weak case a temporal logic with past time modalities is required. The symbolic characterization establishes that, in principle, barbed congruence for such languages can be checked ef...
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...
NonInterleaving Semantics for Mobile Processes
 Theoretical Computer Science
, 1995
"... This paper studies causality in ßcalculus. Our notion of causality combines the dependencies given by the syntactic structure of processes with those originated by passing names. Our studies show that two transitions not causally related may however occur in a fixed ordering in any computation, i.e ..."
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Cited by 41 (19 self)
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This paper studies causality in ßcalculus. Our notion of causality combines the dependencies given by the syntactic structure of processes with those originated by passing names. Our studies show that two transitions not causally related may however occur in a fixed ordering in any computation, i.e., ßcalculus may implicitly express a precedence between actions. Our causality relation still induces the same partial order of transitions for all the computations that are obtained by shuffling transitions that are concurrent (i.e. related neither by causality nor by precedence). Other noninterleaving semantics are investigated and compared. The presentation takes advantage from a parametric definition of process behaviour given in an SOS style. All the results on bisimulationbased equivalences, congruences, axiomatizations and logics are taken (almost) without modifications from the interleaving theory. Finally, we extend our approach to higherorder ßcalculus, enriched with a spawn ...
Causality for Mobile Processes
 In Proceedings of ICALP'95, LNCS 944
, 1995
"... Abstract. We study causality in the ßcalculus. Our notion of causality combines the dependencies given by the syntactic structure of processes with those originated by passing names. It turns out that two transitions not causally related may although occur in a fixed ordering in any computation, i. ..."
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Cited by 29 (18 self)
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Abstract. We study causality in the ßcalculus. Our notion of causality combines the dependencies given by the syntactic structure of processes with those originated by passing names. It turns out that two transitions not causally related may although occur in a fixed ordering in any computation, i.e., ßcalculus may express implicitly a priority between actions. Our causality relation still induces the same partial order of transitions for all the computations that are obtained by shuffling transitions that are concurrent (= related neither by causality nor by priority). The presentation takes advantage from a parametric definition of process behaviour that highlights the essence of the topic. All the results on bisimulation based equivalences, congruences, axiomatizations and logics are taken (almost) for free from the interleaving theory. 1 Introduction The study of the behaviour of a distributed system may benefit from knowledge on the causal relation between its events. For examp...
Timing and Causality in Process Algebra
 Acta Informatica
, 1992
"... . There has been considerable controversy in concurrency theory between the `interleaving' and `true concurrency' schools. The former school advocates associating a transition system with a process which captures concurrent execution via the interleaving of occurrences; the latter adopts more comple ..."
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Cited by 27 (0 self)
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. There has been considerable controversy in concurrency theory between the `interleaving' and `true concurrency' schools. The former school advocates associating a transition system with a process which captures concurrent execution via the interleaving of occurrences; the latter adopts more complex semantic structures to avoid reducing concurrency to interleaving. In this paper we show that the two approaches are not irreconcilable. We define a timed process algebra where occurrences are associated with intervals of time, and give it a transition system semantics. This semantics has many of the advantages of the interleaving approach; the algebra admits an expansion theorem, and bisimulation semantics can be used as usual. Our transition systems, however, incorporate timing information, and this enables us to express concurrency: merely adding timing appropriately generalises transition systems to asynchronous transition systems, showing that time gives a link between true concurrenc...
Locality and Noninterleaving Semantics in calculi for mobile processes
 Theoretical Computer Science
, 1994
"... Process algebra semantics can be categorised into noninterleaving semantics, where parallel composition is considered a primitive operator, and interleaving semantics, where concurrency is reduced to sequentiality plus nondeterminism. The former have an appealing intuitive justification, but the la ..."
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Cited by 23 (4 self)
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Process algebra semantics can be categorised into noninterleaving semantics, where parallel composition is considered a primitive operator, and interleaving semantics, where concurrency is reduced to sequentiality plus nondeterminism. The former have an appealing intuitive justification, but the latter are mathematically more tractable. This paper addresses the study of noninterleaving semantics in the framework of process algebras for mobile systems, like calculus [MPW92, Mil91]. We focus on location bisimulation ( ` ), in our opinion one of the most convincing noninterleaving equivalences, which aims to describe the spatial dependencies on processes. We introduce ` in calculus following the definition for CCS given in [BCHK91b]. Our main contribution is to show that in calculus ` can be expressed, or implemented, within the ordinary interleaving observation equivalence [Mil89, MPW92] by means of a fairly simple and fully abstract encoding. Thus, we can take advantage of the...
Observing Distribution in Processes: Static and Dynamic Localities
, 1994
"... The distributed structure of CCS processes can be made explicit by assigning different locations to their parallel components. The assignment of locations may be done statically, or dynamically as the execution proceeds. The dynamic approach was developed first, by Boudol et al., as it appeared more ..."
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Cited by 15 (1 self)
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The distributed structure of CCS processes can be made explicit by assigning different locations to their parallel components. The assignment of locations may be done statically, or dynamically as the execution proceeds. The dynamic approach was developed first, by Boudol et al., as it appeared more convenient for defining notions of location equivalence and preorder. Extending previous work by L. Aceto we study here the static approach, which is more natural from an intuitive point of view, and more manageable for verification purposes. We define static notions of location equivalence and preorder, and show that they coincide with the dynamic ones. To establish the equivalence of the two location semantics, we introduce an intermediate transition system called occurrence system, which incorporates both notions of locality. This system supports a definition of local history preserving bisimulation for CCS, which is a third formulation of location equivalence.
Causality and True Concurrency: A Dataflow Analysis of the PiCalculus (Extended Abstract)
, 1995
"... ) (Appeared in the Proceedings of the Fourth International Conference on Algebraic Methodology and Software Technology, July 1995 Lecture Notes in Computer Science, Volume 936) Lalita Jategaonkar Jagadeesan Software Production Research Dept. AT&T Bell Laboratories Naperville, IL 60566 (USA) lalita ..."
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Cited by 12 (0 self)
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) (Appeared in the Proceedings of the Fourth International Conference on Algebraic Methodology and Software Technology, July 1995 Lecture Notes in Computer Science, Volume 936) Lalita Jategaonkar Jagadeesan Software Production Research Dept. AT&T Bell Laboratories Naperville, IL 60566 (USA) lalita@research.att.com Radha Jagadeesan ? Math. Sciences Loyola University Chicago, IL 60626 (USA) radha@math.luc.edu 1 Introduction The picalculus [18, 17] is a process algebra for describing networks of processes with dynamically evolving communication structure. The key idea underlying the picalculus is the notion of naming: names are used to refer to channels  the links between processes, and can be dynamically created or hidden. Names together with a rich algebra of process combinators that includes parallel composition, allow the picalculus to encode asynchronous networks of processes that evolve dynamically. In turn, mobility  this ability to change the network configuratio...