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Reactive Systems, Barbed Semantics, and the Mobile Ambients
"... Reactive systems, proposed by Leifer and Milner, represent a metaframework aimed at deriving behavioral congruences for those specification formalisms whose operational semantics is provided by rewriting rules. Despite its applicability, reactive systems suffered so far from two main drawbacks. Fir ..."
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Reactive systems, proposed by Leifer and Milner, represent a metaframework aimed at deriving behavioral congruences for those specification formalisms whose operational semantics is provided by rewriting rules. Despite its applicability, reactive systems suffered so far from two main drawbacks. First of all, no technique was found for recovering a set of inference rules, e.g. in the socalled SOS style, for describing the distilled observational semantics. Most importantly, the efforts focussed on strong bisimilarity, tackling neither weak nor barbed semantics. Our paper addresses both issues, instantiating them on a calculus whose semantics is still in a flux: Cardelli and Gordon’s mobile ambients. While the solution to the first issue is tailored over our case study, we provide a general framework for recasting (weak) barbed equivalence in the reactive systems formalism. Moreover, we prove that our proposal captures the behavioural semantics for mobile ambients proposed by Rathke and Sobociński and by Merro and Zappa Nardelli.
Reactive Systems, (Semi)Saturated Semantics and Coalgebras on Presheaves
, 2009
"... The semantics of process calculi has traditionally been specified by labelled transition systems (ltss), but with the development of name calculi it turned out that reaction rules (i.e., unlabelled transition rules) are often more natural. This leads to the question of how behavioural equivalences ( ..."
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Cited by 8 (1 self)
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The semantics of process calculi has traditionally been specified by labelled transition systems (ltss), but with the development of name calculi it turned out that reaction rules (i.e., unlabelled transition rules) are often more natural. This leads to the question of how behavioural equivalences (bisimilarity, trace equivalence, etc.) defined for lts can be transferred to unlabelled transition systems. Recently, in order to answer this question, several proposals have been made with the aim of automatically deriving an lts from reaction rules in such a way that the resulting equivalences are congruences. Furthermore these equivalences should agree with the standard semantics, whenever one exists. In this paper we propose saturated semantics, based on a weaker notion of observation and orthogonal to all the previous proposals, and we demonstrate the appropriateness of our semantics by means of two examples: logic programming and open Petri nets. We also show that saturated semantics can be efficiently characterized through the so called semisaturated games. Finally, we provide coalgebraic models relying on presheaves.
Coalgebraic Symbolic Semantics
"... The operational semantics of interactive systems is usually described by labeled transition systems. Abstract semantics (that is defined in terms of bisimilarity) is characterized by the final morphism in some category of coalgebras. Since the behaviour of interactive systems is for many reasons in ..."
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Cited by 5 (2 self)
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The operational semantics of interactive systems is usually described by labeled transition systems. Abstract semantics (that is defined in terms of bisimilarity) is characterized by the final morphism in some category of coalgebras. Since the behaviour of interactive systems is for many reasons infinite, symbolic semantics were introduced as a mean to define smaller, possibly finite, transition systems, by employing symbolic actions and avoiding some sources of infiniteness. Unfortunately, symbolic bisimilarity has a different “shape” with respect to ordinary bisimilarity, and thus the standard coalgebraic characterization does not work. In this paper, we introduce its coalgebraic models.
On Barbs and Labels in Reactive Systems
, 2010
"... Reactive systems (RSs) represent a metaframework aimed at deriving behavioral congruences for those computational formalisms whose operational semantics is provided by reduction rules. RSs proved a flexible specification device, yet so far most of the efforts dealing with their behavioural semantic ..."
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Cited by 3 (3 self)
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Reactive systems (RSs) represent a metaframework aimed at deriving behavioral congruences for those computational formalisms whose operational semantics is provided by reduction rules. RSs proved a flexible specification device, yet so far most of the efforts dealing with their behavioural semantics focused on idem pushouts (IPOs) and saturated (also known as dynamic) bisimulations. In this paper we introduce a novel, intermediate behavioural equivalence: Lbisimilarity, which is able to recast both its IPO and saturated counterparts. The equivalence is parametric with respect to a set L of RSs labels, and it is shown that under mild conditions on L it is indeed a congruence. Furthermore, Lbisimilarity can also recast the notion of barbed semantics for RSs, proposed by the same authors in a previous paper. In order to provide a suitable testbed, we instantiate our proposal by addressing the semantics of (asynchronous) CCS and of the calculus of mobile ambients.
Making the unobservable, unobservable
 ICE 2008
, 2008
"... Behavioural equivalences of various calculi for modelling distributed systems differ significantly because the properties which can be observed through interaction depend heavily upon their mode of communication. A typical approach to describing the semantics of communicating processes is to provide ..."
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Cited by 2 (1 self)
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Behavioural equivalences of various calculi for modelling distributed systems differ significantly because the properties which can be observed through interaction depend heavily upon their mode of communication. A typical approach to describing the semantics of communicating processes is to provide a labelled transition system (lts) which captures the interaction potential of the individual processes within a larger system. In many cases, a natural rendering of this lts leads to too fine a semantics as unobservability of certain communications is not accounted for. We propose that a standard approach to augmenting ltss allows morally unobservable communications to actually be modelled as unobservables in the semantics. This approach derives from a rule initially given by Honda and Tokoro to account for unobservability of reception in the asynchronous πcalculus. We examine the implications of adding such rules to lts with respect to the proving behavioural equivalences for various synchronisation mechanisms.
BISIMILARITY IN CONCURRENT CONSTRAINT PROGRAMMING
, 2010
"... In this doctoral work we aim at developing a new approach to labelled semantics and equivalences for the Concurrent Constraint Programming (CCP) which will enable a broader capture of processes behavioural equivalence. Moreover, we work towards exploiting the strong connection between first order ..."
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In this doctoral work we aim at developing a new approach to labelled semantics and equivalences for the Concurrent Constraint Programming (CCP) which will enable a broader capture of processes behavioural equivalence. Moreover, we work towards exploiting the strong connection between first order logic and CCP. Something which will allow us to represent logical formulae in terms of CCP processes and verify its logical equivalence by means of our notion of bisimilarity. Finally, following the lines of the Concurrecy Workbench we plan to implement a CCP Workbench based on our theoretical structure.
Saturated LTSs for Adhesive Rewriting Systems
, 2010
"... GReactive Systems (GRSs) are a framework for the derivation of labelled transition systems (LTSs) from a set of unlabelled rules. A label for a transition from A to B is a context C[−] such that C[A] may perform a reaction and reach B. If either all contexts, or just the “minimal” ones, are conside ..."
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GReactive Systems (GRSs) are a framework for the derivation of labelled transition systems (LTSs) from a set of unlabelled rules. A label for a transition from A to B is a context C[−] such that C[A] may perform a reaction and reach B. If either all contexts, or just the “minimal” ones, are considered, the resulting LTS is called saturated (GIPO, respectively). The borrowed contexts (BCs) technique addresses the issue in the setting of the DPO approach. Indeed, from an adhesive rewriting system (ARS) a GRS can be defined such that DPO derivations correspond to reactions, and BC derivations to transitions of the GIPO LTS. This paper extends the BCs technique in order to derive saturated LTSs for ARSs, applying it to capture bisimilarity for asynchronous calculi.
Under consideration for publication in Math. Struct. in Comp. Science Concurrency Can’t Be Observed, Asynchronously †
, 2012
"... The paper is devoted to an analysis of the concurrent features of asynchronous systems. A preliminary step is represented by the introduction of a noninterleaving extension of barbed equivalence. This notion is then exploited in order to prove that concurrency cannot be observed through asynchronou ..."
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The paper is devoted to an analysis of the concurrent features of asynchronous systems. A preliminary step is represented by the introduction of a noninterleaving extension of barbed equivalence. This notion is then exploited in order to prove that concurrency cannot be observed through asynchronous interactions, i.e., that the interleaving and concurrent versions of a suitable asynchronous weak equivalence actually coincide. The theory is validated on some case studies, related to nominal calculi (πcalculus) and visual specification formalisms (Petri nets). Additionally, we prove that a class of systems which are (outputbuffered) asynchronous according to a characterisation previously proposed in the literature falls into our theory.
SYMBOLIC AND ASYNCHRONOUS SEMANTICS VIA NORMALIZED COALGEBRAS ∗
, 2010
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