Towards a systematic process for modelling complex systems in event-B

Abstract

Formal methods are mathematical techniques used for developing large systems. The complexity of growing systems pose an increasing challenge in the task of formal development and requires a significant improvement of formal techniques and tool support.

Event-B is a formal method used for modelling and reasoning about systems. The Rodin platform is an open tool that supports Event-B specification and verification. This research aims to address some challenges in modelling complex systems. The main challenges addressed in this thesis cover three aspects: The first aspect focuses on providing a way to manage the complexity of large systems. The second aspect focuses on bridging the gap between the requirements and the formal models. The third aspect focuses on supporting the reuse of models and their proofs.

To address the first challenge, we have attempted to simplify the task of formal development of large systems using a compositional technique. The compositional technique aims at dividing the system into smaller parts starting from requirements, followed on by a construction of the specification of each part in isolation, and then finally composing these parts together to model the overall behaviour of the system. We classified the requirements into two categories: The first category consists of a different set of requirements, each of which describes a particular component of the system. The second category describes the composition requirements that show how components interact with each other. The first category is used to construct Event-B specification of each component separately from other components. The second category is used to show the interaction of the separated models using the composition technique.

To address the second and the third challenges, we proposed two techniques in this thesis. The first technique supports construction of a formal model from informal requirements with the aim of retaining traceability to requirements in models. This approach makes use of the UML-B and atomicity decomposition (AD) approaches. UML-B provides the UML graphical notation that enables the development of an Event-B formal model, while the AD approach provides a graphical notation to illustrate the refinement structures and assists in the organisation of refinement levels. The second technique supports the reusability of Event-B formal models and their respective proof obligations. This approach adopts generic instantiation and composition approaches to form a new methodology for reusing existing Event-B models into the development process of other models. Generic instantiation technique is used to create an instance of a pattern that consists of refinement chain in a way that preserves proofs while composition is used to enable the integration of several sub-models into a large model. FreeRTOS (real-time operating system) was selected as a case study to identify and address the above mentioned general problems in the formal development of complex systems.

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Identifiers

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

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