Fault-tolerant bisimulation and process transformations

2000

When verifying concurrent systems described by transition systems, state explosion is one of the most serious problems. If quantitative temporal information (expressed by clock ticks) is considered, state explosion is even more serious. We present a notion of abstraction of transition systems, where the abstraction is driven by the formulae of a quantitative temporal logic, called qu-mu-calculus, defined in the paper. The abstraction is based on a notion of bisimulation equivalence, called ρ, n -equivalence, where ρ is a set of actions and n is a natural number. It is proved that two transition systems are ρ, n -equivalent iff they give the same truth value to all qu-mu-calculus formulae such that the actions occurring in the modal operators are contained in ρ, and with time constraints whose values are less than or equal to n. We present a non-standard (abstract) semantics for a timed process algebra able to produce reduced transition systems for checking formulae. The abstract semantics, parametric with respect to a set ρ of actions and a natural number n, produces a reduced transition system ρ, nequivalent to the standard one. A transformational method is also defined, by means of which it is possible to syntactically transform a program into a smaller one, still preserving ρ, n -equivalence.

DAIMI Report Series, 1993

This thesis is concerned with the verification of concurrent systems modelled by process algebras. It provides methods and techniques for reasoning about temporal properties as described by assertions from an expressive modal logic -- the modal µ-calculus. It describes a compositional approach to model checking, efficient local and global algorithms for model checking finite-state systems, a general local fixed-point finding algorithm, a proof system for model checking infinite-state systems, a categorical completeness result for an intuitionistic version of the modal µ-calculus, and finally it shows some novel applications of the logic for expressing behavioural relations.

Algebraic Foundations of Systems Specification, 1999

This article presents an extension of the formalism of algebraic specifications to the specification of concurrent systems. The key concept is that of process specifications, which have two hierarchical layers: processes and data. Processes apply to data via an application operator, eventually yielding a set of data as a result. Syntax and semantics of process specifications are presented, with emphasis on methodological issues (how to write hierarchically consistent and complete specifications). A suitable notion of observational congruence is introduced and characterized. A notion of implementation is denned, and a general method for proving correction is considered, based on the notion of serializability proof. A primitive for putting specifications together, in parellel, is analyzed. Finally, richer primitives for building basic specifications are discussed. Our proposal is illustrated via several examples inciuding the one of the systematic, stepwise development of a complex specification. * Partially supported by the Esprit 432 METEOR project.

Information and Computation, 1995

Computer Networks and ISDN Systems, 1993

A system is described which supports proofs of both behavioural and logical properties of concurrent systems; these are specified by means of a process algebra and its associated logics. The logic is an action based version of the branching time logic CTL which we call ACTL; it is interpreted over transition labelled structures while CTL is interpreted over state labelled ones. The core of the system are two existing tools, AUTO and EMC. The f'wst builds the labelled transition system corresponding to a term of a process algebra and permits proof of equivalence and simplification of terms, while the second chocks validity of CTL logical formulae. The integration is realized by memos of two translation functions from the action based branching time logic ACTL to CTL and from transition-labelled to state-labelled structures. The correctness of the integration is guaranteed by the proof that the two functions when coupled preserve satisfiability of logical formulae.

Information Processing Letters, 1992

Luo, G., G. v. Bochmann, A. Das and C. Wu, Failure-equivalent transformation of transition systems to avoid internal actions, Information Processing Letters 44 (1992) 333-343.

Formal Methods in System Design, 1995

We study property preserving transformations for reactive systems. The main idea is the use of simulations parameterized by Galois connections (α, γ), relating the lattices of properties of two systems. We propose and study a notion of preservation of properties expressed by formulas of a logic, by a function α mapping sets of states of a systemS into sets of states of a systemS'. We give results on the preservation of properties expressed in sublanguages of the branching time μ-calculus when two systemsS andS' are related via (α, γ)-simulations. They can be used to verify a property for a system by verifying the same property on a simpler system which is an abstraction of it. We show also under which conditions abstraction of concurrent systems can be computed from the abstraction of their components. This allows a compositional application of the proposed verification method. This is a revised version of the papers [2] and [16]; the results are fully developed in [28].

The Computer Journal, 1998

CSP and Petri Nets are powerful formalisms for the specification and the analysis of concurrent systems. We present an approach to their integration to take advantage of both formalisms. In particular the GSPN class is used to address dependability and real-time aspects. In this paper an algorithmic transformation from a trace-based specification of a concurrent system to a Petri Net model is described. Causal dependencies between behaviours of the system components are introduced in the net model through the definition of external assumptions. The steps of the integration are illustrated by applying them to an unmanned transportation problem.

Procedia Computer Science, 2016

The process-oriented design and implementation of concurrent systems have important advantages. However, it is challenging to verify the consistency of process communications between the design and the implementation. To deal with such a challenge, we construct a formal framework for designing, implementing and verifying the consistency of process communications. In this framework, we use Failures in Communicating Sequential Processes (CSP), Erasmus and Category Theory as the foundation. The framework is illustrated by using a running example.

This paper introduces different views for understanding problems and faults with the goal of defining a method for the formal specification of systems. The idea of Layered Fault Tolerant Specification (LFTS) is proposed to make the method extensible to fault tolerant systems. The principle is layering the specification in different levels, the first one for the normal behavior and the others for the abnormal. The abnormal behavior is described in terms of an Error Injector (EI) which represents a model of the erroneous interference coming from the environment. This structure has been inspired by the notion of idealized fault tolerant component but the combination of LFTS and EI using Rely/Guarantee reasoning to describe their interaction can be considered as a novel contribution. The progress toward this method and this way to organize fault tolerant specifications has been made experimenting on case studies and an example is presented.