4 lation and optimization. These are essential constituents of the
iterative process, leading to a feasible and, one hopes, optimal design.
1.3 Content of the Book In Chapter 2 we present briefly the history of
CAD. The main components of CAD systems are identified, and their
principal functions described. Economi- cal and interdisciplinary
aspects are discussed. Chapter 3 starts with a systems analysis of the
design process. The notion of a process is introduced as a fundamental
tool to describe activities like design as a whole, computer-aided
design, program executions, terminal sessions etc. The environment and
the resources which the environment must supply for the successful
execution of any process are discussed. The problem of modelling the
design objects in an abstract schema and the interrelation between the
schema and the planning of the individual step in the design are
analysed. Chapter 4 concentrates on the interfaces among the components
of a CAD system, including the human operator. The problem of mapping an
abstract schema onto the capabilities of various programming, command,
or data de- scription languages is described in detail. Emphasis is laid
upon the resource aspect and its influence on the design of CAD systems.
The concept of a CAD software machine is introduced, and rules for
designing such machines are given.