Abstract. This note addresses the history of process algebra as an area of research in concurrency theory, the theory of parallel and distributed systems in computer science. Origins are traced back to the early seventies of the twentieth century, and developments since that time are sketched. The author gives his personal views on these matters. He also considers the present situation, and states some challenges for the future.

µCRL [13] is a language for specifying and verifying distributed systems in an algebraic fashion. It targets the specification of system behaviour in a process-algebraic style and of data elements in the form of abstract data types. The µCRL toolset [21] (see

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The VoDka server is a video-on-demand system for a Spanish cable company. We look at the distributed scheduler of this system. This scheduler enables that whenever a user agent is asking for a certain movie, this request is transferred through the system and a set of possible play-back qualities is returned to the agent. In case of a non-empty set, the agent selects one and the movie is streamed to the user.

This document describes an automated theorem prover, based on an extension of binary decision diagrams.

Abstract. We present a new method for fighting the state space explosion of process algebraic specifications, by performing static analysis on an intermediate format: linear process equations (LPEs). Our method consists of two steps: (1) we reconstruct the LPE’s control flow, detecting control flow parameters that were introduced by linearisation as well as those already encoded in the original specification; (2) we reset parameters found to be irrelevant based on data flow analysis techniques similar to traditional liveness analysis, modified to take into account the parallel nature of the specifications. Our transformation is correct with respect to strong bisimilarity, and never increases the state space. Case studies show that impressive reductions occur in practice, which could not be obtained automatically without reconstructing the control flow. 1

Abstract—This paper presents a novel linear processalgebraic format for probabilistic automata. The key ingredient is a symbolic transformation of probabilistic process algebra terms that incorporate data into this linear format while preserving strong probabilistic bisimulation. This generalises similar techniques for traditional process algebras with data, and — more importantly — treats data and data-dependent probabilistic choice in a fully symbolic manner, paving the way to the symbolic analysis of parameterised probabilistic systems. Keywords-probabilistic process algebra, linearisation, datadependent probabilistic choice, symbolic transformations I.

Two different lines of research are presented in the study of an industrially relevant problem of impact control. One is focused on actual control of the process, while the other is focused on the development of a general language for modeling hybrid systems, of which the case study is an appropriate example.

We describe the toolset for the behavioural specification language mCRL2. The purpose of the toolset is to analyse abstract models that describe the communication behaviour of software based systems. With the help of the toolset we want to efficiently detect and prevent problems in software, preferably before it is built. The tools allow to transform specifications, generate and visualise state spaces, verify modal properties, and much more. In order to facilitate reuse of the code most of the functionality is included in libraries. This makes the toolset suitable as a platform for third party tool development and for other specification languages as well. The toolset is distributed under the Boost license, which permits such use.

Abstract. We present a probabilistic leader election algorithm for anonymous, bidirectional, asynchronous rings. It is based on an algorithm from Franklin [22], augmented with random identity selection, hop counters to detect identity clashes, and round numbers modulo 2. As a result, the algorithm is finite-state, so that various model checking techniques can be employed to verify its correctness, that is, eventually a unique leader is elected with probability one. We also sketch a formal correctness proof of the algorithm for rings with arbitrary size. 1