Algorithm Extraction

Abstract

We are now in a position to start assembling a chain of processes which can be used to transfine the specification of a function into a scheme for its implementation; for the implementation of a program which, given suitable data, can be executed to calculate the function. In most cases we shall have to use a mix of different design strategies for transformation and refinement. So far we have only met (reversible) transformations — refinement comes later — and so we shall have to make specific structure choices which will preserve the deterministic nature of our specifications. In Chapters 4 and 5, we shall be able to handle non-deterministic specifications and introduce general decomposition methods (which must then be particularised to make the resultant design deterministic — i.e. we must choose from a set of alternatives and this then involves an irreversible step in which some superfluous information is, intentionally, discarded).