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14
Bisimilarity of Open Terms
, 2000
"... Traditionally, in process calculi, relations over open terms, i.e., terms with free process variables, are defined as extensions of closedterm relations: two open terms are related if and only if all their closed instantiations are related. Working in the context of bisimulation, in this paper we s ..."
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Traditionally, in process calculi, relations over open terms, i.e., terms with free process variables, are defined as extensions of closedterm relations: two open terms are related if and only if all their closed instantiations are related. Working in the context of bisimulation, in this paper we study a different approach; we define semantic models for open terms, socalled conditional transition systems, and define bisimulation directly on those models. It turns out that this can be done in at least two different ways, one giving rise to De Simone's formal hypothesis bisimilarity and the other to a variation which we call hypothesispreserving bisimilarity (denoted t fh and t hp, respectively). For open terms, we have (strict) inclusions t fh /t hp / t ci (the latter denoting the standard ``closed instance' ' extension); for closed terms, the three coincide. Each of these relations is a congruence in the usual sense. We also give an alternative characterisation of t hp in terms of nonconditional transitions, as substitutionclosed bisimilarity (denoted t sb). Finally, we study the issue of recursion congruence: we prove that each of the above relations is a congruence with respect to the recursion operator; however, for t ci this result holds under more restrictive conditions than for tfh and thp.]
Graph Rewriting, Constraint Solving and Tiles for Coordinating Distributed Systems
 Applied Categorical Structures
, 1999
"... . In this paper we describe an approach to model the dynamics of distributed systems. For distributed systems we mean systems consisting of concurrent processes communicating via shared ports and posing certain synchronization requirements, via the ports, to the adjacent processes. The basic idea is ..."
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Cited by 17 (14 self)
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. In this paper we describe an approach to model the dynamics of distributed systems. For distributed systems we mean systems consisting of concurrent processes communicating via shared ports and posing certain synchronization requirements, via the ports, to the adjacent processes. The basic idea is to use graphs to represent states of such systems, and graph rewriting to represent their evolution. The kind of graph rewriting we use is based on simple contextfree productions which are however combined by means of a synchronization mechanism. This allows for a good level of expressivity in the system without sacrifying full distribution. To formally model this kind of graph rewriting, however, we do not adopt the classical graph rewriting style but a more general framework, called the tile model, which allows for a clear separation between sequential rewriting and synchronization. Then, since the problem of satisfying the synchronization requirements may be a complex combinatorial pro...
Tile Bisimilarity Congruences for Open Terms and Term Graphs
 in: Proc. CONCUR 2000, LNCS 1877 (2000
, 2000
"... The definition of sos formats ensuring that bisimilarity on closed terms is a congruence has received much attention in the last two decades. For dealing with open system specifications, the congruence is usually lifted from closed terms to open terms by instantiating the free variables in all possi ..."
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Cited by 13 (7 self)
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The definition of sos formats ensuring that bisimilarity on closed terms is a congruence has received much attention in the last two decades. For dealing with open system specifications, the congruence is usually lifted from closed terms to open terms by instantiating the free variables in all possible ways; the only alternatives considered in the literature relying on Larsen and Xinxin's context systems and Rensink's conditional transition systems. We propose a different approach based on tile logic, where both closed and open terms are managed analogously. In particular, we analyze the `bisimilarity as congruence' property for several tile formats that accomplish di erent concepts of subterm sharing.
An Interactive Semantics of Logic Programming
 THEORY AND PRACTICE OF LOGIC PROGRAMMING
, 2001
"... We apply to logic programming some recently emerging ideas from the field of reductionbased communicating systems, with the aim of giving evidence of the hidden interactions and the coordination mechanisms that rule the operational machinery of such a programming paradigm. The semantic framework we ..."
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Cited by 8 (6 self)
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We apply to logic programming some recently emerging ideas from the field of reductionbased communicating systems, with the aim of giving evidence of the hidden interactions and the coordination mechanisms that rule the operational machinery of such a programming paradigm. The semantic framework we have chosen for presenting our results is tile logic, which has the advantage of allowing a uniform treatment of goals and observations and of applying abstract categorical tools for proving the results. As main contributions, we mention the finitary presentation of abstract unification, and a concurrent and coordinated abstract semantics consistent with the most common semantics of logic programming. Moreover, the compositionality of the tile semantics is guaranteed by standard results, as it reduces to check that the tile systems associated to logic programs enjoy the tile decomposition property. An extension of the approach for handling constraint systems is also discussed.
CCS Semantics via Proved Transition Systems and Rewriting Logic
 In Kirchner and Kirchner [47
, 1998
"... We consider (a slight variant of) the ccs calculus, and we analyze two operational semantics defined in the literature: the first exploits Proved Transition Systems (pts) and the second Rewriting Logic (rl). We show that the interleaving interpretation of both semantics agree, in that they define th ..."
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We consider (a slight variant of) the ccs calculus, and we analyze two operational semantics defined in the literature: the first exploits Proved Transition Systems (pts) and the second Rewriting Logic (rl). We show that the interleaving interpretation of both semantics agree, in that they define the same transitions and exhibit the same nondeterministic structure. In addition, we study causality in ccs computations. We recall the treatment via pts, that exhibits the notion of causality presented in the literature, and we show how to recast it in the rl semantics via suitable axioms. 1 Introduction Concurrency is maybe the basic aspect of the operational interpretation of rewriting logic. And as Jos'e Meseguer says in his lecture at concur'96 [20], . . . my main emphasis in this talk will be on rewriting logic as a semantic framework for concurrency. . . . The goal is . . . to express as faithfully as possible each model [of concurrency] on its own terms, avoiding any encodings or tr...
A causal semantics for CCS via rewriting logic
, 2002
"... We consider two operational semantics for CCS de ned in the literature: the first exploits proved transition systems (PTS) and the second rewriting logic (RL). We show that the interleaving interpretation of both semantics agree, in that they define the same transitions and exhibit the same nondete ..."
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Cited by 7 (0 self)
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We consider two operational semantics for CCS de ned in the literature: the first exploits proved transition systems (PTS) and the second rewriting logic (RL). We show that the interleaving interpretation of both semantics agree, in that they define the same transitions and exhibit the same nondeterministic structure. In addition, we study causality in CCS computations. We recall its treatment via PTS, exhibiting the notion of causality presented in the literature, and we show how to recast it in the RL semantics via suitable axioms. Also in this case, the two
Logical Specification of Operational Semantics
 IN CSL'99, PROC. CONF. ON COMPUTER SCIENCE LOGIC, VOLUME 1683 OF LNCS
, 1999
"... Various logicbased frameworks have been proposed for specifying the operational semantics of programming languages and concurrent systems, including inference systems in the styles advocated by Plotkin and by Kahn, Horn logic, equational specifications, reduction systems for evaluation contexts ..."
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Cited by 4 (3 self)
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Various logicbased frameworks have been proposed for specifying the operational semantics of programming languages and concurrent systems, including inference systems in the styles advocated by Plotkin and by Kahn, Horn logic, equational specifications, reduction systems for evaluation contexts, rewriting logic, and tile logic. We consider
Modeling Process Coordination Via Tiles, Graphs, And Constraints
, 1998
"... In this paper we describe a simple approach where distributed systems' dynamics is expressed via synchronized graph rewriting. We formalize this approach via the tile model, which is a general framework providing a formal description of coordination and synchronization among processes. Finally, ..."
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In this paper we describe a simple approach where distributed systems' dynamics is expressed via synchronized graph rewriting. We formalize this approach via the tile model, which is a general framework providing a formal description of coordination and synchronization among processes. Finally, to efficiently solve the synchronization problem, which in some cases can be a complex combinatorial problem, we use techniques for constraint solving and propagation. INTRODUCTION Distributed systems are usually asynchronous, but some level of synchronization is needed to make possible basic activities as message reception. In practice, a key role is often played by more complex kinds of coordination, like transactions, distributed problem solving or computersupported collaborative work. In this paper, we present a simple model of computation for a class of distributed systems which can be described by using synchronized graph rewriting. The reason we use graphs and graph rewriting systems [3...
Can Actors and πAgents Live Together?
"... The syntax and semantics of actors and agents is first defined separately, using a uniform, "unbiased" approach. New coordination primitives are the added to the union of the two calculi which allow actors and agents to cooperate. ..."
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The syntax and semantics of actors and agents is first defined separately, using a uniform, "unbiased" approach. New coordination primitives are the added to the union of the two calculi which allow actors and agents to cooperate.