Deriving Specifications from Requirements: An Example

Abstract

A requirement is a desired relationship among phenomena of the environment of a system, to be brought about by the hardware/software machine that will be constructed and installed in the environment.A specification describes machine behaviour sufficient to achieve the requirement.A specification is a restricted kind of requirement all the environment phenomena mentioned in a specitlcation are shared with the machinq the phenomena constrained by the speciilcation are controlled by the machine; and the specified constraints can be determined without reference to the future.Specflcations are derived from requirements by reasoning about the environtnen~using properties that hold independently of the behaviour of the machine.These ideas, and some associated techniques of description, are illustrated by a simple example.