A State-Based Characterisation of the Conflict Preorder

This paper proposes a way to effectively compare the potential of processes to cause conflict. In discrete event systems theory, two concurrent systems are said to be in conflict if they can get trapped in a situation where they are both waiting or running endlessly, forever unable to complete their common task. The conflict preorder is a process-algebraic pre-congruence that compares two processes based on their possible conflicts in combination with other processes. This paper improves on previous theoretical descriptions of the conflict preorder by introducing less conflicting pairs as a concrete state-based characterisation. Based on this characterisation, an effective algorithm is presented to determine whether two processes are related according to the conflict preorder.Comment: In Proceedings FOCLASA 2011, arXiv:1107.584

Conflict-preserving abstraction of discrete event systems using annotated automata

This paper proposes to enhance compositional verification of the nonblocking property of discrete event systems by introducing annotated automata. Annotations store nondeterministic branching information, which would otherwise be stored in extra states and transitions. This succinct representation makes it easier to simplify automata and enables new efficientmeans of abstraction, reducing the size of automata to be composed and thus the size of the synchronous product state space encountered in verification. The abstractions proposed are of polynomial complexity, and they have been successfully applied to model check the nonblocking property of the same set of large-scale industrial examples as used in related work

Hierarchical modelling of manufacturing systems using discrete event systems and the conflict preorder

This paper introduces Hierarchical Interface-Based Supervisory Control using the Conflict Preorder and applies it to the design of two manufacturing systems models of practical scale. Hierarchical Interface-Based Supervisory Control decomposes a large system into subsystems linked to each other by interfaces, facilitating the design of complex systems and the re-use of components. By ensuring that each subsystem satisfies its interface consistency conditions locally, it can be ensured that the complete system is controllable and nonblocking. The interface consistency conditions proposed in this paper are based on the conflict preorder, providing increased flexibility over previous approaches. The framework requires only a small number of interface consistency conditions, and allows for the design of multi-level hierarchies that are provably controllable and nonblocking

Fair Subtyping for Multi-Party Session Types

The subtyping relation defined for dyadic session type theories may compromise the liveness of multi-party sessions. In this paper we define a fair subtyping relation for multi-party session types that preserves liveness, we relate it with the subtyping relation for dyadic session types, and we provide coinductive, axiomatic, and algorithmic characterizations for it

Fair Subtyping for Multi-party Session Types

International audienceWe study a theory of session types in which we add a liveness property to the familiar safety one. In this setting, some subtype relations between session types that hold in other theories and that are commonly regarded as harmless become unsound. We present various equivalent definitions of the subtyping relation, we relate it with the standard ones, and we give algorithms for deciding it. Incidentally, we provide an original and remarkably simple coinductive characterization of the fair testing preorder for nondeterministic, sequential processes consisting of internal choices of outputs and external choices of inputs

On Conflicts in Concurrent Systems

This dissertation studies conflicts. A conflict is a bug in concurrent systems where one or more components of the system may potentially be blocked from completing their task. This dissertation investigates how nonconflicting completions may be used to characterise the situations in which individual components of a system may be in conflict with other components. The first major contributions of this dissertation are new methods of abstracting systems with respect to conflicts, and showing how these methods may be used to check whether a large system is conflict-free. The second contribution is a method of comparing whether one system is less susceptible to conflict than another. The last major contribution is a method of expressing all conflicts in a system in a finite and canonical way. The methods developed have applications for model checking, refinement, and the development of contracts for concurrent systems