Author

# W. P. Weijland

Bio: W. P. Weijland is an academic researcher. The author has contributed to research in topics: Cellular algebra & Differential graded algebra. The author has an hindex of 1, co-authored 1 publications receiving 1055 citations.

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01 Jan 1990

TL;DR: A hybrid process algebra can be used for the specification, simulation, control and verification of embedded systems in combination with the environment, and for any dynamic system in general.

Abstract: Process algebra is the study of distributed or parallel syst em by algebraic means. Originating in computer science, process algebra has been extended in re ce t years to encompass not just discrete-event systems, but also continuously evolving ph enomena, resulting in so-called hybrid process algebras. A hybrid process algebra can be used for th e specification, simulation, control and verification of embedded systems in combination with the ir environment, and for any dynamic system in general. As the vehicle of our exposition, we use th e hybrid process algebra χ (Chi). The syntax and semantics of χ are discussed, and it is explained how equational reasoning simplifies tool implementations for simulation and verification. A bot tle filling line example is introduced to illustrate system analysis by means of equational reasonin g.

1,058 citations

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01 Jan 1996

TL;DR: This book familiarizes readers with important problems, algorithms, and impossibility results in the area, and teaches readers how to reason carefully about distributed algorithms-to model them formally, devise precise specifications for their required behavior, prove their correctness, and evaluate their performance with realistic measures.

Abstract: In Distributed Algorithms, Nancy Lynch provides a blueprint for designing, implementing, and analyzing distributed algorithms. She directs her book at a wide audience, including students, programmers, system designers, and researchers.
Distributed Algorithms contains the most significant algorithms and impossibility results in the area, all in a simple automata-theoretic setting. The algorithms are proved correct, and their complexity is analyzed according to precisely defined complexity measures. The problems covered include resource allocation, communication, consensus among distributed processes, data consistency, deadlock detection, leader election, global snapshots, and many others.
The material is organized according to the system model-first by the timing model and then by the interprocess communication mechanism. The material on system models is isolated in separate chapters for easy reference.
The presentation is completely rigorous, yet is intuitive enough for immediate comprehension. This book familiarizes readers with important problems, algorithms, and impossibility results in the area: readers can then recognize the problems when they arise in practice, apply the algorithms to solve them, and use the impossibility results to determine whether problems are unsolvable. The book also provides readers with the basic mathematical tools for designing new algorithms and proving new impossibility results. In addition, it teaches readers how to reason carefully about distributed algorithms-to model them formally, devise precise specifications for their required behavior, prove their correctness, and evaluate their performance with realistic measures.
Table of Contents
1 Introduction
2 Modelling I; Synchronous Network Model
3 Leader Election in a Synchronous Ring
4 Algorithms in General Synchronous Networks
5 Distributed Consensus with Link Failures
6 Distributed Consensus with Process Failures
7 More Consensus Problems
8 Modelling II: Asynchronous System Model
9 Modelling III: Asynchronous Shared Memory Model
10 Mutual Exclusion
11 Resource Allocation
12 Consensus
13 Atomic Objects
14 Modelling IV: Asynchronous Network Model
15 Basic Asynchronous Network Algorithms
16 Synchronizers
17 Shared Memory versus Networks
18 Logical Time
19 Global Snapshots and Stable Properties
20 Network Resource Allocation
21 Asynchronous Networks with Process Failures
22 Data Link Protocols
23 Partially Synchronous System Models
24 Mutual Exclusion with Partial Synchrony
25 Consensus with Partial Synchrony

4,340 citations

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01 Jan 1993TL;DR: The π-calculus is a model of concurrent computation based upon the notion of naming that is generalized from monadic to polyadic form and semantics is done in terms of both a reduction system and a version of labelled transitions called commitment.

Abstract: The π-calculus is a model of concurrent computation based upon the notion of naming. It is first presented in its simplest and original form, with the help of several illustrative applications. Then it is generalized from monadic to polyadic form. Semantics is done in terms of both a reduction system and a version of labelled transitions called commitment; the known algebraic axiomatization of strong bisimilarity is given in the new setting, and so also is a characterization in modal logic. Some theorems about the replication operator are proved.

1,016 citations

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TL;DR: This paper investigates whether observation equivalence really does respect the branching structure of processes, and finds that in the presence of the unobservable action τ of CCS this is not the case, and the notion of branching bisimulation equivalence is introduced which strongly preserves the branching structures of processes.

Abstract: In comparative concurrency semantics, one usually distinguishes between linear time and branching time semantic equivalences. Milner's notion of observatin equivalence is often mentioned as the standard example of a branching time equivalence. In this paper we investigate whether observation equivalence really does respect the branching structure of processes, and find that in the presence of the unobservable action t of CCS this is not the case.Therefore, the notion of branching bisimulation equivalence is introduced which strongly preserves the branching structure of processes, in the sense that it preserves computations together with the potentials in all intermediate states that are passed through, even if silent moves are involved. On closed CCS-terms branching bisimulation congruence can be completely axiomatized by the single axion scheme: a.(t.(y+z)+y)=a.(y+z) (where a ranges over all actions) and the usual loaws for strong congruence.We also establish that for sequential processes observation equivalence is not preserved under refinement of actions, whereas branching bisimulation is.For a large class of processes, it turns out that branching bisimulation and observation equivalence are the same. As far as we know, all protocols that have been verified in the setting of observation equivalence happen to fit in this class, and hence are also valid in the stronger setting of branching bisimulation equivalence.

851 citations

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TL;DR: In this article, the authors propose inheritance-preserving transformation rules for workflow processes and show that these rules can be used to avoid problems such as the "dynamic change bug." The dynamic change bug refers to errors introduced by migrating a case (i.e., a process instance) from an old process definition to a new one.

550 citations

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01 Jan 2001TL;DR: Various semantics in the linear time - branching time spectrum are presented in a uniform, model-independent way, and for each of them a complete axiomatization is provided.

Abstract: In this paper various semantics in the linear time - branching time spectrum are presented in a uniform, model-independent way. Restricted to the class of finitely branching, concrete, sequential processes, only fifteen of them turn out to be different, and most semantics found in the literature that can be defined uniformly in terms of action relations coincide with one of these fifteen. Several testing scenarios, motivating these semantics, are presented, phrased in terms of ‘button pushing experiments’ on generative and reactive machines. Finally twelve of these semantics are applied to a simple language for finite, concrete, sequential, nondeterministic processes, and for each of them a complete axiomatization is provided.

525 citations