Pattern-Oriented Software Architecture: A Pattern Language for Distributed Computing, 4th Volume

Chapter 1. On Patterns and Pattern Languages

Neither can embellishment of language be found without arrangement and expression of thoughts, nor can thoughts be made to shine without the light of language.

Marcus Tullius Cicero, Roman stateman, orator, and philosopher, 106–43 BC

In this chapter we introduce patterns briefly, including their history, along with a number of pattern concepts. We examine the anatomy of a pattern, what it offers, and what drives it. We explore the relationships we often find between patterns. We conclude with a discussion of pattern languages, what they are, and how they can be presented and used.

Patterns Introduced

From a design perspective, software is often thought of in terms of its parts: functions, source files, modules, objects, methods, classes, packages, libraries, components, services, subsystems, and so on. These all represent valid views of the different kinds and scales of units of composition with which developers work directly. These views focus on the parts, however, and de-emphasize the broader relationships and the reasoning that make a design what it is. In contrast, patterns have become a popular and complementary way of describing and evolving software designs, capturing and naming proven and common techniques. They emphasize the why, where, and how of designs, not just the what.

A pattern documents a recurring problem–solution pairing within a given context. A pattern, however, is more than either just the problem or just the solution ...