Extending the B Method with Distribution

The B method, developed by Abrial1, is a formal method for the development of provably correct computer systems. In the B method, a system is specified as an abstract machine consisting of some state and some operations acting on that state. This is essentially the same structure as an action system2 which describes the behaviour of a parallel reactive system in terms of the atomic actions (i.e., operations) that can take place during its execution. Refinement is a technique for developing correct implementations of formal specifications. As with B abstract machines, action systems may be refined in a stepwise manner. Techniques for refining the atomicity of operations and for composing systems in parallel have been developed for action systems and such techniques are important for the development of parallel/distributed systems. This paper describes an approach to the design of distributed systems that combines action systems and B.