Functional software design and its graphical representation

Abstract

The concept of a functional unit with several entries and an internal state is proposed as basic concept for the functional design of programs that are executed in a single sequential process. Four basic principles are formulated: the inclusion principle and the dissection principle govern the composition of a functional unit. whereas the modification principle and the symmetry principle govern the modifications of the internal state. Three graphic design representations are demonstrated: Activation diagrams specify the various levels of integration between the basic machine and the complete system. Status diagrams and activation flow charts represent the legal sequences of calls for the various entries of a functional unit. The sequence of these calls is constrained due to their interaction with the internal state. The practicability of the concepts, principles, and graphic representation schemes is demonstrated in two examples: a simple file system and a data management subsystem of a finite element software package.