Rob van Glabbeek

Omer Keskin, Nobuko Yoshida, Rob van Glabbeek

Multiparty session types (MPST) offer a framework for the description of communication-based protocols involving multiple participants. In the top-down approach to MPST, the communication pattern of the session is described using a global type. Then the global type is projected on to a local type for each participant, and the individual processes making up the session are type-checked against these projections. Typed sessions possess certain desirable properties such as safety, deadlock-freedom and liveness. In this work, we present the first mechanised proof of liveness for synchronous multiparty session types in the Rocq Proof Assistant. Building on recent work, we represent global and local types as coinductive trees using the paco library. We use a coinductively defined subtyping relation on local types together with another coinductively defined plain-merge projection relation relating local and global types. We then associate collections of local types, or local type contexts, with global types using this projection and subtyping relations, and prove an operational correspondence between a local type context and its associated global type. We utilise this association relation to prove the safety and liveness of associated local type contexts and, consequently, the multiparty sessions typed by these contexts. Besides clarifying the often informal proofs found in the MPST literature, our Rocq mechanisation also enables the certification of liveness properties of communication protocols. Our contribution amounts to around 14K lines of Rocq code, available at https://github.com/omerskeskin/mpstlive .

Yu Wang, Zhaohui Zhu, Rob van Glabbeek et al.

In order to guarantee that a supervised system satisfies safety requirements of the specification, as well as requirements saying that in certain states certain events must be enabled, this paper introduces required events for discrete event systems and reconsiders the similarity control problem while taking all requirements from the specification into account. The notion of a covariant-contravariant simulation, which is finer than the conventional notion of simulation, is adopted to act as the behavioral relation of supervisory control theory. A necessary and sufficient condition for the solvability of this problem is established and a method for synthesizing a maximally permissive supervisor is provided.

Rob van Glabbeek, Bas Luttik, Myrthe Spronck

We verify the correctness of a variety of mutual exclusion algorithms through model checking. We look at algorithms where communication is via shared read/write registers, where those registers can be atomic or non-atomic. For the verification of liveness properties, it is necessary to assume a completeness criterion to eliminate spurious counterexamples. We use justness as completeness criterion. Justness depends on a concurrency relation; we consider several such relations, modelling different assumptions on the working of the shared registers. We present executions demonstrating the violation of correctness properties by several algorithms, and in some cases suggest improvements.

Rob van Glabbeek, Jan Friso Groote, Peter Höfner

This volume contains the proceedings of MARS 2015, the first workshop on Models for Formal Analysis of Real Systems, held on November 23, 2015 in Suva, Fiji, as an affiliated workshop of LPAR 2015, the 20th International Conference on Logic for Programming, Artificial Intelligence and Reasoning. The workshop emphasises modelling over verification. It aims at discussing the lessons learned from making formal methods for the verification and analysis of realistic systems. Examples are: (1) Which formalism is chosen, and why? (2) Which abstractions have to be made and why? (3) How are important characteristics of the system modelled? (4) Were there any complications while modelling the system? (5) Which measures were taken to guarantee the accuracy of the model? We invited papers that present full models of real systems, which may lay the basis for future comparison and analysis. An aim of the workshop is to present different modelling approaches and discuss pros and cons for each of them. Alternative formal descriptions of the systems presented at this workshop are encouraged, which should foster the development of improved specification formalisms.