Bert Lisser

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.

A Database Approach to Distributed State-Space Generation

We study distributed state-space generation on a cluster of workstations. It is explained why state-space partitioning by a global hash function is problematic when states contain variables from unbounded domains, such as lists or other recursive data types. Our solution is to introduce a database which maintains a global numbering of state values. We also describe tree compression, a technique of recursive state folding, and show that it is superior to manipulating plain state vectors. This solution is implemented and linked to the µCRL toolset, where state values are implemented as maximally shared terms (ATerms). However, it is applicable to other models as well, e.g. PROMELA or LOTOS models. Our experiments show the trade-offs between keeping the database global, replicated or local, depending on the available network bandwidth and latency.

Distributed Extended Beam Search for Quantitative Model Checking

In this paper, we mainly focus on solving scheduling problems with model checking, where a finite number of entities needs to be processed as efficiently as possible, for instance by a machine. To solve these problems, we model them in untimed process algebra, where time is modelled using a special tickaction. We propose a set of distributed state space explorations to find schedules for the modelled problems, building on the traditional notion of beam search. The basic approach is called distributed (detailed) beam search, which prunes parts of the state space while searching using an evaluation function in order to find near-optimal schedules in very large state spaces. Variations on this approach are presented, such as distributed flexible, distributed g-synchronised, and distributed prioritybeam search, which can also practically be used in combinations.

Compressed and Distributed File Formats for Labeled Transition Systems

Abstract With model checking techniques growing towards maturity, the availability for standardised file formats for labeled transition systems is more important than ever. A number of requirements for file formats are introduced, based on requirements for software, databases and compression. Two candidate formats, SVC I and SVC II are introduced, with the former emphasising compression and the latter focusing on distributed access. The two formats are compared with existing file formats.

New developments around the mCRL tool set

Abstract Some recent developments in the μCRL tool set are presented. New analysis techniques are a symbolic model checker, and a visualizer for huge state spaces. Also various transformations are presented. At symbolic level, theorem proving, data flow analysis, and confluence checking are used to obtain considerable state space reductions. At the concrete level, distributed implementations of state space generation and minimization are recent. We mention the successful application of the tools to the verification of large data-intensive distributed systems.

Distributed Partial Order Reduction for Security Protocols

We describe a distributed partial order reduction algorithm for security protocols. Some experimental results using an implementation of the algorithm in the distributed @mCRL toolset are also reported.

Distributed analysis with µCRL: a compendium of case studies

Models in process algebra with abstract data types can be analysed by state space generation and reduction tools. The µCRL toolset implements a suite of distributed verification tools for clusters of workstations. We illustrate their application to large case studies from a wide range of application areas, such as functional analysis, scheduling, security analysis, test case generation and game solving.

Towards Formal Verification of ToolBus Scripts

ToolBus allows one to connect tools via a software bus. Programming is done using the scripting language Tscript , which is based on the process algebra ACP. Tscript was originally designed to enable formal verification, but this option has so far not been explored in any detail. We present a method for analyzing a Tscript by translating it to the process algebraic language mCRL2, and then applying model checking to verify behavioral properties.

Coordination of a parallel proposition solver

In this paper we describe an experiment in which MANIFOLD is used to coordinate the interprocess communication in a parallelized proposition solver. MANIFOLD is very well suited for applications involving dynamic process creation and dynamically changing (ir)regular communication patterns among sets of independent concurrent cooperating processes. The idea in this case study is simple. The proposition solver consists of a fixed numbers of separate processing units which communicate with each other such that the output of one serves as the input for the other. Because one of the processing units performs a computation intensive job, we introduce a master/worker protocol to divide its computations. We show that this protocol implemented in MANIFOLD adds another hierarchic layer to the application but leaves the previous layers intact. This modularity of MANIFOLD offers the possibility to introduce concurrency step by step. We also verify the implementation of the proposition solver using a simple family of assertions and give some performance results.

Automated translation and analysis of a ToolBus script for auctions

ToolBus allows to connect tools via a software bus. Programming is done using the scripting language Tscript, which is based on the process algebra ACP. In previous work we presented a method for analyzing a Tscript by translating it to the process algebraic language mCRL2, and then applying model checking to verify certain behavioral properties. We have implemented a prototype based on this approach. As a case study, we have applied it on a standard example from the ToolBus distribution, distributed auction, and detected a number of behavioral irregularities in this auction Tscript.