Software structuring principles for VLSI CAD

It is argued that systems should be designed for reusability by anticipating change. This goal can be achieved by designing the software by layers of problem-oriented languages, which are implemented by suitably extending a base language. A language layer rarely needs to be adapted to changes, only the application (i.e. algorithm) has to be changed. The authors illustrate this methodology with respect to VLSI CAD programs and a particular language layer: a language for handling networks. Such a language consists of a base language (EC or Lisp) plus data types, operations and control structures that are relevant to network problems. The network language is but one of several languages used; other languages used deal with sets, two-dimensional layout structures, waveforms, etc. The discussion of the network language illustrates this technique