On Event-B and Control Flow

Abstract

Event-B is a general purpose formal development method suitable for the design and detailed development of safety-critical systems. Being a data-driven formalism, it lacks any control flow constructs. This turns out to be a limitation for systems with rich control flow properties. In Event-B, control flow information has to be embedded into guards and event actions and this results in an entanglement of control flow and functional specification with the additional downside of extra model variables. This paper proposes a method for extending Event-B models with an new viewpoint portraying control flow properties of a model. The novelty of the work is in relying solely on theorem proving to demonstrate the consistency of control flow and main Event-B specification. The focus is placed on the practicality of working with such an extension and also on achieving proof economy. A detailed formal treatment of the method is presented and illustrated with a case study. A proof of concept implementation for the RODIN platform is briefly discussed.