From requirement document to formal modelling and decomposition of control systems

Abstract

Formal modelling of control systems can help with identifying missing requirements and design flaws before implementing them. However, modelling using formal languages can be challenging and time consuming. Therefore intermediate steps may be required to simplify the transition from informal requirements to a formal model.

In this work we firstly provide a four-stage approach for structuring and formalising requirements of a control system. This approach is based on monitored, controlled, mode and commanded (MCMC) phenomena. In this approach, requirements are partitioned into MCMC sub-problems, which then will be formalised as independent sub-models. The formal language used in this thesis is Event-B, although the MCMC approach can be applied to other formal languages. We also provide guidelines and patterns which can be used to facilitate the process of modelling in the Event-B language.

The second contribution of this work is to extend the structure of machines in Event-B language and provide an approach for composing the formal MCMC sub-models in order to obtain the overall specification. The composition deals with phenomena that are shared amongst the formal sub-models. In our third contribution, patterns and guidelines are provided to refine the overall formal specification further in order to define design details. In addition, we discuss the decomposition of a formal model of a control system.

As practical examples, the MCMC approach is applied to the requirements of three automotive control systems, namely a cruise control system, a lane departure warning system, and a lane centering controller.

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Identifiers

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

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