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Application of the Four Variable Model to a CAD System for Microwave
Communications Devices

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Mr. Yun Zou

Abstract

This report studies the application of the four-variable
requirements model to a CAD system for microwave communications
systems (CADMCS), a complex non-real-time software package. The
documentation of the complete system requirements for the CADMCS
system is presented.

The four variable model is reviewed in detail. Based on the
characteristics of CAD systems, the techniques to control the
complexity using the well-known principles such as
information-hiding, separation of concerns or divide-and-conquer
are discussed. The use of well-known mathematical concepts such
as vectors, vector functions, as well as geometry objects as the
types of the monitored and controlled variables is demonstrated.
A new classification of the monitored and controlled variables is
also introduced to make the documentation easier to understand
and serve as the mechanism to support a hierarchical system
structure.

This work demonstrates the recursive decomposition of the
monitored and controlled variables. Relational algebra has been
applied to presenting and organizing the REQ (requirements)
relation in the CADMCS system. The report shows how complex
relations can be described in terms of simpler sub-relations
using the decomposition operator of relational algebra.