Description of Essential System Behaviour using Message-state Tables

This paper describes a step-by-step method for reaching agreement between the client and the software builder concerning how a system should interact with its user. The method springs from the view of McMenamin and Palmer that all physical systems have both essential behaviour (what is to be done) and physical behaviour (how it is to be done) and that it is useful to define the essential behaviour before discussing how to implement it using real hardware and software. The method leads to an essential system behaviour guide that combines completeness and brevity; it encourages client and builder to share the task of describing essential system behaviour in a language that both can understand. The method is illustrated for the case of a system that manipulates elements and sets.