Capsules

Abstract

Well organized large systems tend to consist of a large number of small pieces of code each of which captures a single semantic unit. These pieces of code are strung together to form larger semantic phrases, which are in turn components of even larger phrases. The smallest semantic units in a polynomial manipulation system might be the routines that add and multiply the coefficients of the polynomials. These routines are combined (used as subroutines) to form the routines that add and multiply polynomials, which are components in the factoring and greatest common divisor routines. When a system is built in a top down manner, the larger phrases are formed first and are used to define the semantic components of the smaller phrases. Bottom up software design begins with the small phrases and generates the large phrases. In practice a combination of these two approaches is often used. The manner in which the routines are initially connected is usually simple, but in time the addition of new capabilities and features, and the necessities of performance enhancement generally cause the dependency structure to become quite complex.