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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 59 (3 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
Vertical Implementation
 Information and Computation
, 2001
"... We investigate criteria to relate specifications and implementations belonging to conceptually different levels of abstraction. For this purpose, we introduce the generic concept of a vertical implementation relation, which is a family of binary relations indexed by a refinement function that maps a ..."
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Cited by 8 (0 self)
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We investigate criteria to relate specifications and implementations belonging to conceptually different levels of abstraction. For this purpose, we introduce the generic concept of a vertical implementation relation, which is a family of binary relations indexed by a refinement function that maps abstract actions onto concrete processes and thus determines the basic connection between the abstraction levels. If the refinement function is the identity, the vertical implementation relation collapses to a standard (horizontal) implementation relation. As desiderata for vertical implementation relations we formulate a number of congruencelike proof rules (notably a structural rule for recursion) that offer a powerful, compositional proof technique for vertical implementation. As a candidate vertical implementation relation we propose vertical bisimulation. Vertical bisimulation is compatible with the standard interleaving semantics of process algebra; in fact, the corresponding horizontal relation is rooted weak bisimulation. We prove that vertical bisimulation satisfies the proof rules for vertical implementation, thus establishing the consistency of the rules. Moreover, we define a corresponding notion of abstraction that strengthens the intuition behind vertical bisimulation and also provides a decision algorithm for finitestate systems. Finally, we give a number of small examples to demonstrate the advantages of vertical implementation in general and vertical bisimulation in particular. 1
On Parallel vs. Sequential Threshold Cellular Automata
 IN PROCEEDINGS OF THE FIRST EUROPEAN CONFERENCE ON COMPLEX SYSTEMS ECCS’05, EUROPEAN COMPLEX SYSTEMS SOCIETY
, 2005
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Syntactic Action Refinement in Presence of Multiway Synchronization
 In proc. of the workshop on Semantics of Specification Languages (SoSL'93
, 1994
"... Action refinement, which consists in replacing actions at a given level of abstraction by processes at a lower level, is considered by many as a fundamental technique for designing complex systems. With this purpose in mind, we show how the problem may be dealt with in presence of multiway synchroni ..."
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Cited by 5 (2 self)
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Action refinement, which consists in replacing actions at a given level of abstraction by processes at a lower level, is considered by many as a fundamental technique for designing complex systems. With this purpose in mind, we show how the problem may be dealt with in presence of multiway synchronization and illustrate our approach by applying it to a language derived from the standardized Formal Description Technique LOTOS [12]. Two solutions are proposed : the first solution does not make any a priori assumption about action atomicity, and the second solution corresponds to a slight modification of the first one, which shows how action atomicity may still be preserved in presence of action refinement. 1 Introduction Action refinement is recognized as a fundamental technique for designing complex systems, as it permits to consider designs at different levels of abstraction. Looking at several ongoing works on action refinement, we can classify the approaches undertaken in two main c...
An EventBased SOS for a Language with Refinement
 Structures in Concurrency Theory, Workshops in Computing
, 1995
"... The notion of action refinement has been studied intensively in the past few years. It is usually introduced in the form of an operator in a process algebraic language, for which a denotational semantics in a suitable model is then given. In this paper we complement this approach by defining a corre ..."
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Cited by 4 (2 self)
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The notion of action refinement has been studied intensively in the past few years. It is usually introduced in the form of an operator in a process algebraic language, for which a denotational semantics in a suitable model is then given. In this paper we complement this approach by defining a corresponding operational semantics for refinement, in the form of derivation rules for a transition relation. Because of the (wellknown) fact that ordinary transition systems are not expressive enough to capture the effects of refinement, we use an eventbased transition system model described elsewhere in the literature. The operational semantics of refinement thus defined is equivalent (in fact event isomorphic) to the usual denotational semantics. 1 Introduction Process algebras form a wellknown specification paradigm for concurrent systems. Typical operators describe such constructions as parallel composition, and such implementation mechanisms as sequential composition. One operator that...
Modeling and Analysis of the Collective Dynamics of LargeScale MultiAgent Systems: A Cellular and Network Automata based Approach
, 2006
"... This technical report addresses a particular approach to modeling and analysis of the behavior of largescale multiagent systems. A broad variety of multiagent systems are modeled as appropriate variants of cellular and network automata. Several fundamental properties of the collective dynamics of ..."
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Cited by 2 (0 self)
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This technical report addresses a particular approach to modeling and analysis of the behavior of largescale multiagent systems. A broad variety of multiagent systems are modeled as appropriate variants of cellular and network automata. Several fundamental properties of the collective dynamics of those cellular and network automata are then formally analyzed. Various loosely coupled largescale distributed information systems are of an increasing interest in a variety of areas of computer science and its applications – areas as diverse as team robotics, intelligent transportation systems, open distributed software environments, disaster response management, distributed databases and information retrieval, and computational theories of language evolution. A popular paradigm for abstracting such distributed infrastructures is that of multiagent systems (MAS) made of typically a large number of autonomous agents that locally interact with each other. This report is an attempt at a cellular and network automata based mathematical and computational theory of such MAS. The
PARALLEL vs. SEQUENTIAL THRESHOLD CELLULAR AUTOMATA: Comparison and Contrast
"... Cellular automata (CA) are an abstract model of a distributed dynamical system, as well as of finegrain parallelism in computing. In a classical cellular automaton, all the nodes execute their operations in parallel and in perfect synchrony. We consider herewith the sequential version of CA, called ..."
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Cellular automata (CA) are an abstract model of a distributed dynamical system, as well as of finegrain parallelism in computing. In a classical cellular automaton, all the nodes execute their operations in parallel and in perfect synchrony. We consider herewith the sequential version of CA, called SCA, and compare those SCA with the classical, parallel CA. In particular, we show that there are 1D CA with very simple node update rules that cannot be simulated by any comparable SCA, irrespective of the node update ordering. Consequently, the granularity of the basic CA operations and, therefore, the finegrain parallelism of the classical, synchronous CA, insofar as the “interleaving semantics” is concerned, turns out to be not fine enough. We also study in some detail the properties of the cellular automata whose nodes update their states according to the Majority update rule. Finally, we share some thoughts on how to extend the presented results, and, in particular, we try to motivate the study of genuinely asynchronous cellular automata.
Automating the Refinement of Specifications for Distributed Systems via Syntactic Transformations
"... The idea of successively refining an abstract specification until it contains enough detail to suggest an implementation has been investigated by numerous researchers. The emphasis to date has been on techniques that, unfortunately, lead to a large amount of manual formal labor for each refinement s ..."
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The idea of successively refining an abstract specification until it contains enough detail to suggest an implementation has been investigated by numerous researchers. The emphasis to date has been on techniques that, unfortunately, lead to a large amount of manual formal labor for each refinement step. With such techniques, both the cost and the possibility of errors arising in formal manipulation are high. Using a theorem prover can reduce the number of manipulation errors, but, given current technology, the amount of labor is still daunting. This research explores an alternative solution to the refinement problem, namely the use of syntactic transformations to realize each refinement step. We reduce formal labor by employing automatic transformations that guarantee the preservation of desirable properties  e.g., deadlockfreedom. Automatic transformations are particularly appealing for the development of large, complex distributed systems, where a manual approach to refinement wo...