Engineering by Software: System Behaviours as Components

Software engineering means developing software for a purpose. For systems that interact with a physical problem world, the proximate purpose is a desired behaviour of that problem world: the fundamental engineering task is to develop the system behaviour and specify the software that will evoke it. This chapter sketches a discipline for this task, in which behaviours are always understood as the result of interactions of a software machine and a physical problem world. Complex behaviour is designed in terms of simple constituent behaviours. The running behaviour instances form a dynamic tree in which control of the tree is exercised by the software machines at the nodes.