Wan Fokkink

µCRL: A Toolset for Analysing Algebraic Specifications

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 http://www.cwi.nl/~mcrl) supports the analysis and manipulation of µCRL specifications. A µCRL specification can be automatically transformed into a linear process operator (LPO). All other tools in the µCRL toolset use LPOs as their starting point. The simulator allows the interactive simulation of an LPO. There are a number of tools that allow optimisations on the level of LPOs. The instantiator generates a labelled transition system (LTS) from an LPO (under the condition that it is finite-state), and the resulting LTS can be visualised, analysed and minimised.

Ntyft/ntyxt Rules Reduce to Ntree Rules

Groote and Vaandrager introduced thetyft/tyxt formatfor Transition System Specifications (TSSs), and established that for each TSS in this format that iswell-founded, the bisimulation equivalence it induces is a congruence. In this paper, we construct for each TSS in tyft/tyxt format an equivalent TSS that consists oftree rulesonly. As a corollary we can give an affirmative answer to an open question, namely whether the well-foundedness condition in the congruence theorem for tyft/tyxt can be dropped. These results extend to tyft/tyxt with negative premises and predicates.

A conservative look at operational semantics with variable binding

We set up a formal framework to describe transition system specifications in the style of Plotkin. This framework has the power to express many-sortedness, general binding mechanisms, and substitutions, among other notions such as negative hypotheses and unary predicates on terms. The framework is used to present a conservativity format in operational semantics, which states sufficient criteria to ensure that the extension of a transition system specification with new transition rules does not affect the semantics of the original terms.

Precongruence formats for decorated trace semantics

This paper explores the connection between semantic equivalences and preorders for concrete sequential processes, represented by means of labeled transition systems, and formats of transition system specifications using Plotkins structural approach. For several preorders in the linear time---branching time spectrum a format is given, as general as possible, such that this preorder is a precongruence for all operators specifiable in that format. The formats are derived using the modal characterizations of the corresponding preorders.

Executing Multicellular Differentiation: Quantitative Predictive Modelling of C. elegans Vulval Development

MOTIVATION Understanding the processes involved in multi-cellular pattern formation is a central problem of developmental biology, hopefully leading to many new insights, e.g. in the treatment of various diseases. Defining suitable computational techniques for development modelling, able to perform in silico simulation experiments, is an open and challenging problem. RESULTS Previously, we proposed a coarse-grained, quantitative approach based on the basic Petri net formalism, to mimic the behaviour of the biological processes during multicellular differentiation. Here, we apply our modelling approach to the well-studied process of Caenorhabditis elegans vulval development. We show that our model correctly reproduces a large set of in vivo experiments with statistical accuracy. It also generates gene expression time series in accordance with recent biological evidence. Finally, we modelled the role of microRNA mir-61 during vulval development and predict its contribution in stabilizing cell pattern formation.

Analyzing a Chi model of a turntable system using Spin, CADP, and Uppaal

Nowadays, due to increasing system complexity and growing competition and costs, industry makes high demands on powerful techniques used to design and analyze manufacturing systems. One of the most popular techniques to do performance analysis is simulation. However, simulation-based analysis cannot guarantee the correctness of a system, so it is less suitable for functional analysis. Our research focuses on examining other methods to do performance analysis and functional analysis, and trying to combine the two. One of the approaches is to translate a simulation model that is used for performance analysis to a model written in an input language of an existing verification tool. We translate a χ [D.A. van Beek, K.L. Man, M.A. Reniers, J.E. Rooda, R.R.H. Schiffelers, Syntax and Consistent Equation Semantics of Hybrid Chi, CS-Report 04-37, Eindhoven University of Technology, 2004] simulation model of a turntable system into models written in the input languages of the tools CADP [J.-C. Fernandez, H. Garavel, A. Kerbrat, L. Mounier, R. Mateescu, M. Sighireanu, CADP—a protocol validation and verification toolbox, in: Proceedings of the 8th Conference on Computer Aided Verification (CAV’96), Lecture Notes in Computer Science, vol. 1102, 1996, pp. 437–440], Spin [G.J. Holzmann, The SPIN Model Checker, Addison-Wesley, 2003] and Uppaal [K.G. Larsen, P. Pettersson, W.Yi, Uppaal in a nutshell, Int. J. Software Tools for Technology Transfer 1 (1–2) (1997) 134–152] and do a functional analysis with each of them. This allows us to evaluate the usefulness of these tools for the functional analysis of χ models. We compare the input formalisms, the expressiveness of the temporal logics, and the algorithmic techniques for model checking that are used in those tools.

MeanField analysis for the evaluation of gossip protocols

Gossip protocols are designed to operate in very large, decentralised networks. A node in such a network bases its decision to interact (gossip) with another node on its partial view of the global system. Because of the size of these networks, analysis of gossip protocols is mostly done using simulations, that tend to be expensive in computation time and memory consumption. We employ mean-¿eld approximation for an analytical evaluation of gossip protocols. Nodes in the network are represented by small identical stochastic models. Joining all nodes would result in an enormous stochastic process. If the number of nodes goes to in¿nity, however, mean-¿eld analysis allows us to replace this intractably large stochastic process by a small deterministic process. This process approximates the behaviour of very large gossip networks, and can be evaluated using simple matrix-vector multiplications.

Rooted Branching Bisimulation as a Congruence

This article presents a congruence format, in structural operational semantics, for rooted branching bisimulation equivalence. The format imposes additional requirements on Grootes ntyft format. It extends an earlier format by Bloom with standard notions such as recursion, iteration, predicates, and negative premises.

Lazy rewriting on eager machinery

The article introduces a novel notion of lazy rewriting. By annotating argument positions as lazy, redundant rewrite steps are avoided, and the termination behavior of a term-rewriting system can be improved. Some transformations of rewrite rules enable an implementation using the same primitives as an implementation of eager rewriting.

Process Algebra with Recursive Operations

Abstract This chapter provides an overview of the addition of various forms of iteration, i.e., recursive operations, to process algebra. Of these operations, (the original, binary version of) the Kleene star is considered most basic, and an equational axiomatisation of its combination with basic process algebra is explained in detail. The focus on iteration in process algebra raised interest in a number of variations of the Kleene star operation, of which an overview, including various completeness and expressivity results, is presented. Though most of these variations concern regular (iterative) operations, also the combination of process algebra and some non-regular operations is discussed, leading to undecidability and stronger expressivity results. Finally, some attention is paid to the interplay between iteration and the special process algebra constants representing the silent step and the empty process.