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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...
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 ...
Refinement of Actions and Equivalence Notions for Concurrent Systems
 Acta Informatica
, 1998
"... This paper combines and extends the material of [GGa/c/d/e], except for the part in [GGc] on refinement of transitions in Petri nets and the discussion of TCSPlike parallel composition in [GGe]. An informal presentation of some basic ingredients of this paper appeared as [GGb]. Among others, th ..."
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Cited by 36 (1 self)
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This paper combines and extends the material of [GGa/c/d/e], except for the part in [GGc] on refinement of transitions in Petri nets and the discussion of TCSPlike parallel composition in [GGe]. An informal presentation of some basic ingredients of this paper appeared as [GGb]. Among others, the treatment of action refinement in stable and nonstable event structures is new. The research reported here was supported by Esprit project 432 (METEOR), Esprit Basic Research Action 3148 (DEMON), Sonderforschungsbereich 342 of the TU Munchen, ONR grant N0001492J1974 and the Human Capital and Mobility Cooperation Network EXPRESS (Expressiveness of Languages for Concurrency). Contents
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...
History Dependent Automata
, 2001
"... In this paper we present historydependent automata (HDautomata in brief). They are an extension of ordinary automata that overcomes their limitations in dealing with historydependent formalisms. In a historydependent formalism the actions that a system can perform carry information generated i ..."
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Cited by 29 (8 self)
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In this paper we present historydependent automata (HDautomata in brief). They are an extension of ordinary automata that overcomes their limitations in dealing with historydependent formalisms. In a historydependent formalism the actions that a system can perform carry information generated in the past history of the system. The most interesting example is calculus: channel names can be created by some actions and they can then be referenced by successive actions. Other examples are CCS with localities and the historypreserving semantics of Petri nets. Ordinary
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...
Models for NamePassing Processes: Interleaving and Causal
 In Proceedings of LICS 2000: the 15th IEEE Symposium on Logic in Computer Science (Santa Barbara
, 2000
"... We study syntaxfree models for namepassing processes. For interleaving semantics, we identify the indexing structure required of an early labelled transition system to support the usual picalculus operations, defining Indexed Labelled Transition Systems. For noninterleaving causal semantics we de ..."
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Cited by 24 (3 self)
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We study syntaxfree models for namepassing processes. For interleaving semantics, we identify the indexing structure required of an early labelled transition system to support the usual picalculus operations, defining Indexed Labelled Transition Systems. For noninterleaving causal semantics we define Indexed Labelled Asynchronous Transition Systems, smoothly generalizing both our interleaving model and the standard Asynchronous Transition Systems model for CCSlike calculi. In each case we relate a denotational semantics to an operational view, for bisimulation and causal bisimulation respectively. We establish completeness properties of, and adjunctions between, categories of the two models. Alternative indexing structures and possible applications are also discussed. These are first steps towards a uniform understanding of the semantics and operations of namepassing calculi.
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...
Action Refinement
 Handbook of Proacess Algebra
, 2000
"... S. All local authors can be reached via email at the address lastname@cs.unibo.it. Questions and comments should be addressed to tradmin@cs.unibo.it. Recent Titles from the UBLCS Technical Report Series 974 An Algebra of Actors, M. Gaspari, G. Zavattaro, May 1997. 975 On the Turing Equivalen ..."
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Cited by 18 (3 self)
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S. All local authors can be reached via email at the address lastname@cs.unibo.it. Questions and comments should be addressed to tradmin@cs.unibo.it. Recent Titles from the UBLCS Technical Report Series 974 An Algebra of Actors, M. Gaspari, G. Zavattaro, May 1997. 975 On the Turing Equivalence of Linda Coordination Primitives, N. Busi, R. Gorrieri, G. Zavattaro, May 1997 (Revised October 1998). 976 A Process Algebraic View of Linda Coordination Primitives, N. Busi, R. Gorrieri, G. Zavattaro, May 1997. 977 Validating a Software Architecture with respect to an Architectural Style, P. Ciancarini, W. Penzo, July 1997. 978 System Support for PartitionAware Network Applications, O. Babaoglu, R. Davoli, A. Montresor, R. Segala, October 1997. 979 Generalized SemiMarkovian Process Algebra, M. Bravetti, M. Bernardo, R. Gorrieri, October 1997. 981 Group Communication in Partitionable Systems: Specification and Algorithms, O. Babao glu, R. Davoli, A. Montresor, April 1998. 982...
HistoryDependent Automata
 ELECTR. NOTES IN TH. COMP. SCI
, 1998
"... In this paper we present historydependent automata (HDautomata in brief). They are an extension of ordinary automata that overcomes their limitations in dealing with historydependent formalisms. In a historydependent formalism the actions that a system can perform carry information generated in ..."
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Cited by 14 (1 self)
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In this paper we present historydependent automata (HDautomata in brief). They are an extension of ordinary automata that overcomes their limitations in dealing with historydependent formalisms. In a historydependent formalism the actions that a system can perform carry information generated in the past history of the system. The most interesting example is calculus: channel names can be created by some actions and they can then be referenced by successive actions. Other examples are CCS with localities and the historypreserving semantics of Petri nets. Ordinary automata are an unsatisfactory operational model for these formalisms: infinite automata are obtained for all the systems with in nite computations, even for very simple ones; moreover, the ordinary definition of bisimulation does not apply in these cases, thus preventing the reusage of standard theories and algorithms. In this paper we show that HDautomata are an adequate model for the historydependent formalisms. We pr...