New bisimulation semantics for distributed systems

2002

We propose a methodology for the analysis of open systems based on process calculi and bisimilarity. Open systems are seen as coordinators (ie terms with place-holders), that evolve when suitable components (ie closed terms) fill in their place-holders. The distinguishing feature of our approach is the definition of a symbolic operational semantics for coordinators that exploits spatial/modal formulae as labels of transitions and avoids the universal closure of coordinators wrt all components.

ArXiv, 2020

We investigate how various forms of bisimulation can be characterised using the technology of logical relations. The approach taken is that each form of bisimulation corresponds to an algebraic structure derived from a transition system, and the general result is that a relation $R$ between two transition systems on state spaces $S$ and $T$ is a bisimulation if and only if the derived algebraic structures are in the logical relation automatically generated from $R$. We show that this approach works for the original Park-Milner bisimulation and that it extends to weak bisimulation, and branching and semi-branching bisimulation. The paper concludes with a discussion of probabilistic bisimulation, where the situation is slightly more complex, partly owing to the need to encompass bisimulations that are not just relations.

Refinement in bisimulation semantics is defined differently from refinement in failure semantics: in bisimulation semantics refinement is based on simulations between labelled transition systems, whereas in failure semantics refinement is based on inclusions between failure systems. There exist however pairs of refinements, for bisimulation and failure semantics respectively, that have almost the same properties. Furthermore, each refinement in bisimulation semantics implies its counterpart in failure semantics, and conversely each refinement in failure semantics implies its counterpart in bisimulation semantics defined on the canonical form of the compared processes.

Information Processing Letters, 1991

… of Networks and …, 2002

The fundamental notion of bisimulation has inspired various notions of system equivalences in concurrency theory. Many notions of bisimulation for various discrete systems have been recently unified in the abstract category theoretical formulation of bisimulation due to Joyal, Nielsen and Winskel. In this paper, we adopt their framework and unify the notions of bisimulation equivalences for discrete, continuous dynamical and control systems. This shows that our equivalence notion is on the right track, but also confirms that abstract bisimulation is general enough to capture equivalence notions in the domain of continuous systems. We believe that the unification of the bisimulation relation for labelled transition systems and dynamical systems under the umbrella of abstract bisimulation, as achieved in this work, is a first step towards a unified approach to modeling of and reasoning about the dynamics of discrete and continuous structures in computer science and control theory.

Bulletin of The European Association for Theoretical Computer Science, 1996

An open collaborative effort has been initiated: to design a common framework for algebraic specification and development of software. The rationale behind this initiative is that the lack of such a common framework greatly hinders the dissemination and application of research results in algebraic specification. In particular, the proliferation of specification languages, some differing in only quite minor ways from each other, is a considerable obstacle for the use of algebraic methods in industrial contexts, making it difficult to exploit standard examples, case studies and training material. A common framework with widespread ac-ceptm~ce throughout the research community is urgently needed. The aim is to base the common framework as much as possible on a critical selection of features that have already been explored in various contexts. The common framework will provide a family of specification languages at different levels: a central, reasonably expressive language, called CASL, for specifying (requirements, design, and architecture of) conventional software; restrictions of CASL to simpler languages, for use primarily in connection with prototyping and verification tools; and extensions of CASL, oriented towards particular programming paradigms, such as reactive systems and object-based systems. It should aiso be possible to embed many existing algebraic specification languages in members of the CASL family. A tentative design for CASL has already been proposed. Task groups are studying its formal semantics, tool support, methodology, and other aspects, in preparation for the finalization of the design.

Lecture Notes in Computer Science, 1994

We provide three methods of verifying concurrent systems which are tolerant of faults in their operating environment-algebraic, logical and transformational. The rst is an extension of the bisimulation equivalence, the second is rooted in the Hennessy-Milner logic, and the third involves transformations of CCS processes. Based on the common semantic model of labelled transition systems, which is also used to model faults, all three methods are proved equivalent for certain classes of faults. ? To be presented at the Third International Symposium \Formal Techniques in Real-Time and Fault-Tolerant Systems", L ubeck, Germany, September 1994. ?? Supported by the University of Warwick, under its Scholarship Scheme for East Europe, and by an Overseas Students Award from CVCP.

Theoretical Computer Science: Exploring New Frontiers of Theoretical Informatics, 2000

The sos formats ensuring that bisimilarity is a congruence often fail in the presence of structural axioms on the algebra of states. Dynamic bisimulation, introduced to characterize the coarsest congruence for ccs which is also a (weak) bisimulation, reconciles the bisimilarity as congruence property with such axioms and with the specification of open ended systems, where states can be reconfigured at run-time, at the cost of an infinitary operation at the meta-level. We show that the compositional framework offered by tile logic is suitable to deal with structural axioms and open ended systems specifications, allowing for a finitary presentation of context closure.

Zenodo (CERN European Organization for Nuclear Research), 2006

Bisimulation can be defined in a simple way using coinductive methods, and has rather pleasant properties. Ready similarity was proposed by Meyer et al. as a way to weakening the bisimulation equivalence thus getting a semantics defined in a similar way, but supported for more reasonable (weaker) observational properties. Global bisimulations were introduced by Frutos et al. in order to study different variants of non-determinism getting, in particular, a semantics under which the internal choice operator becomes associative. Global bisimulations are defined as plain bisimulations but allowing the use of new moves, called global transitions, that can change the processes not only locally in its head, but anywhere. Now we are continuing the study of global bisimulation but focusing on the way different semantics can be characterised as global bisimulation semantics. In particular, we have studied ready similarity, on the one hand because it was proposed as the strongest reasonable semantics weaker than bisimulation; on the other hand, because ready similarity was not directly defined as an equivalence relation but as the nucleus of an order relation, and this open the question whether it is also possible to define it as a symmetric bisimulation-like semantics. We have got a simple and elegant characterisation of ready similarity as a global bisimulation semantics, that provides a direct symmetric characterisation of it as an equivalence relation, without using any order as intermediate concept. Besides, we have found that it is not necessary to start from a simulation based semantics to get an equivalent global bisimulation. What has proved to be very useful is the axiomatic characterisation of the semantics. Following these ideas we have got also global bisimulation for several semantics, including refusals and traces. That provides a general framework that allows to relate both intensional and extensional semantics.

Lecture Notes in Computer Science, 1993