modularity – Louise Pryor

Good software must be maintainable. It is very rarely the case that a piece of software is developed once and then never nedds to be changed again during its lifetime. This is especially true of user-developed software such as spreadsheets, whose big advantage is that they are easily modified.

Even if the requirements do not change, any reasonably sized piece of software is most unlikely to work properly at first; changes will have to be made in order to remove bugs. In fact, the whole process of development can be seen as one of maintenance, starting from a situation in which nothing works at all.

In the worst case, a simple change requires the whole piece of software to be rewritten from scratch. In the best case, really quite significant changes to the functionality require only small changes in the code. The secret is to write good code and to document it effectively. In this context, good code is code that uses techniques of abstraction and modularity.

Resources

The following external links are relevant:

Managing the operational risks of user-developed software

Modular systems are usually easier to maintain and update, as well as being faster to develop in the first place. So what is modularity?

A modular system is one that consists of a number of small, coherent, chunks (or modules) each of which is self-contained and has a well-defined interface.

Modularity is the single attribute of software that allows a program to be intellectually manageable.
G Myers, 1978

Modularity helps to reduce complexity. A modular system can be understood in terms of the individual modules, without having to grasp all the details at once. Modularity thus provides abstraction.

If the module boundaries are drawn appropriately, modifications to the system are often confined to one or two modules, thus simplifying the modification process.

Another advantage of modularity is that it facilitates code reuse. Again, if the modules are well defined, a single module can be used in several different systems, thus reducing the need to reinvent the wheel.