Muck van Weerdenburg

From µCRL to mCRL2 : motivation and outline

We sketch the language mCRL2, the successor of μCRL, which is a process algebra with data, devised in 1990 to model and study the behaviour of interacting programs and systems. The language is improved in several respects guided by the experience obtained from numerous applications where realistic systems have been modelled and analysed. Just as with μCRL, the leading principle is to provide a minimal set of primitives that allow effective specifications, that conform to standard mathematics and that allow standard mathematical manipulations and proof methodologies. In the first place the equational abstract datatypes have been enhanced with higher-order constructs and standard data types, ranging from booleans, numbers and lists to sets, bags and higher-order function types. In the second place multi-actions have been introduced to allow a seamless integration with Petri nets. In the last place communication is made local to enable compositionality.

Search algorithms for automated validation

A novel search technique called highway search is introduced. The search technique relies on a highway simulation which takes several homogeneous walks through a (possibly infinite) state space. Furthermore, we provide a memory-efficient algorithm that approximates a highway search and we prove that, under particular conditions, they coincide. The effectiveness of highway search is compared to two mainstream search techniques, viz. random search and randomised depth-first search. Our results demonstrate that randomised depth-first search explores the least amount of states in the effort of finding states of interest, whereas a highways search yields the shortest witnessing traces to such states.

Automating Soundness Proofs

When developing a new language with semantics described by Structural Operational Semantics (SOS), one often wants an axiomatisation of this language (w.r.t. to some equivalence) as well. We describe a method for automating the straightforward soundness proofs for the axioms of such an axiomatisation.

Structural Operational Semantics with First-Order Logic

We define a formalism for Structural Operational Semantics (SOS) with first-order-logic formulas as premises. It is shown that in most uses (including all practical uses) this formalism has the same expressivity as SOS without first-order logic. Furthermore, we give a congruence format for (strong) bisimilarity. The latter is shown to be strongly related to the ntyft/ntyxt format.

An Account of Implementing Applicative Term Rewriting

Generation of labelled transition systems from system specifications is highly dependent on efficient rewriting (or related techniques). We give an account of the implementation of two rewriters of the mCRL2 toolset. These rewriters work on open terms and use nonlinear match trees. A comparison is made with other commonly used efficient rewriters.

Action Abstraction in Timed Process Algebra

This paper discusses action abstraction in timed process algebras. It is observed that the leading approaches to action abstraction in timed process algebra all maintain the timing of actions, even if these actions are abstracted from. This paper presents a novel approach to action abstraction in timed process algebras. Characteristic for this approach is that in abstracting from an action, also its timing is abstracted from. We define an abstraction operator and a timed variant of rooted branching bisimilarity and establish that this notion is an equivalence relation and a congruence.

Process Algebra with Local Communication

In process algebras like @mCRL and ACP communication is defined globally. In the context of component-based architectures one wishes to define subcomponents of a system separately, including communication within that subcomponent. We define a process algebra with an operator for local communication that facilitates component-based architectures. Besides being compositional, this language is aimed to be a more practical language (with respect to closely related languages) and also allows for straightforward modelling of synchronous as well as asynchronous behaviour.