Chapter 1 introduces the basic concept of a process as a mathematical abstraction of the interactions between a system and its environment. It shows how the familiar technique of recursion may be used to describe processes that last a long time, or forever. The concepts are explained first by example and then by pictures; a more complete explanation is given by algebraic laws, and by an implementation on a computer in a functional programming language.
The second part of the chapter explains how the behaviour of a process can be recorded as a trace of the sequence of actions in which it engages. Many useful operations on traces are defined. A process can be specified in advance of implementation by describing the properties of its traces. Rules are given to help in implementation of processes which can be proved to meet their specifications.