E.P. de Vink

Jan Friso Groote, Erik P. de Vink

This article gives a historical overview of the background, motivation and development of μCRL and its successor mCRL2, from the inception to the present. Both mCRL2 and μCRL are similar, compact, but very expressive formalisms based on process algebra, term rewriting, and the modal mu-calculus. They are developed to model and analyse the behaviour of interacting systems, i.e., systems that communicate by exchange of messages, among each other and with the outside world. Every contemporary computer system can be viewed as such an interacting system and their communication schemes are difficult to design correctly. By sticking to the mathematical foundations, but being led by the desire to be practically relevant, the formalism has grown to become very versatile. In particular, mCRL2 does not only foster the development of theory and the formulation of correctness proofs, but it is also the basis of a large set of automatic tools that help to provide insight in the behaviour of complex computer controlled systems.

Vincenzo Ciancia, Jan Friso Groote, Diego Latella et al.

Spatial models are of increasing interest in traditional computer science domains and beyond. Spatial minimisation procedures are crucial for efficient model checking of such models that are often large in size. For the recent notion of spatial bisimilarity for quasi-discrete closure models, called `Compatible Paths' (CoPa) bisimilarity, an effective minimisation method is proposed, and shown to be correct. Reasoning about space represented by quasi-discrete closure models involves two different conditional reachability modalities: a forward reachability, similar to that used in temporal logic, and a backward modality, representing the fact that a point can be reached from another point, under certain conditions. The core of our minimisation method is the encoding of closure models as labelled transition systems, enabling minimisation algorithms for branching bisimilarity to compute CoPa equivalence classes. A prototype toolchain, VoxMinX, is proposed to validate the minimisation method. VoxMinX preserves the relationship between equivalence classes and sets of pixels in the original image. Experimental validation of the toolchain via benchmark examples demonstrates a promising speed-up in model checking of spatial properties for models of realistic size.

Herbert Wiklicky, Erik de Vink

This volume of the EPTCS contains the proceedings of the 15th international workshop on Qualitative Aspects of Programming Languages and Systems, QAPL 2017, held at April 23, 2017 in Uppsala, Sweden as a satellite event of ETAPS 2017, the 20th European Joint Conferencec on Theory and Practice of Software. The volume contains two invited contributions by Erika Abraham and by Andrea Vandin as well as six technical papers selected by the QAPL 2017 program committee.