An approach to atomicity decomposition in the Event-B formal method

Abstract

Formal methods are mathematically based techniques and tools to model software and hardware systems. Event-B is a formal method that emerged over the last decade as an evolution of classical B. Event-B is supported by an open and extensible Eclipse-based tool-set, called Rodin. Rodin provides an integrated environment supporting the whole process of multi-stage modelling and handling of the associated proofs. Rodin extensibility is exploited by developing a number of plug-ins to extend the main platform capabilities. During recent years, Event-B and Rodin have been used to model some real-world complex systems and prove consistency properties of them. However developing models of large and complex systems is not an easy task, since it can result in complex models and difficult proofs. There are some techniques in Event-B which can help to tackle the difficulties of modelling complex systems; refinement and model decomposition are two examples. Atomicity decomposition was recently introduced as another technique to help with the structuring of refinement-based development of complex systems in Event-B.

In this research, we have investigated how the development process with Event-B can be enriched further by using the atomicity decomposition approach. The atomicity decomposition approach provides a graphical notation to structure refinement and to support the explicit sequencing of events in an Event-B model. In this approach, modelling usually starts with a single atomic event of the system which is split to two or more sub-events in the next refinement level.

We have further developed the atomicity decomposition patterns and features. A formal description of the atomicity decomposition language is presented. The transformation rules from an atomicity decomposition diagram to the Event-B model are defined. The atomicity decomposition diagrams can be transformed to Event-B models using these rules. Exploiting the extensibility of the Rodin platform, a Rodin plug-in tool was developed to provide atomicity decomposition support in Event-B. The modelling and tool extensions developed in this thesis are applied to two complex case studies, the Media Channel System and the BepiColombo System. We present an evaluation of the atomicity decomposition approach using insights gained from these case studies.

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Identifiers

ORCID for Michael Butler: orcid.org/0000-0003-4642-5373

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