This review describes research work which is just starting in the Electrical Engineering Department of Heriot-Watt University. It is based on a directed-graph method of describing the structure of a computation, and as such can be equally applied to hardware and software. It is a computer aid to the logical and program designer, rather than to the drawing office and production department, like most present day digital c.a.d, systems. The project is based on the results of various workers, and much of this paper contains a summary of their work as a necessary introduction.
It is possible to write a good many pages 1 on the lack of c.a.d, for computer designers: the shortest summary is to say that it is not possible to be sure what a normal hardware logic structure will do except by simulation or exhaustive tests. The alternatives for n Boolean variables must have some relation to 22n, a number which can rapidly outstrip any speed improvement in computer simulation as n increases. Since programming uses hardware-built functions there is a similar effect, and once again the structure of a program is no guarantee of correct performance-exhaustive testing or whether exhaustive testing or machine simulation is needed. Lastly, since the design methods are so different for programs and logic there is a considerable interface problem.