Overview

Previously, I described how design patterns can be used at both the local and global levels. At local levels, patterns tell us how to solve particular problems within the context of the patterns. At global levels, patterns create a map of how the components of the application interrelate with one another. One way to study design patterns is to learn how to use them more effectively at both the local and global levels. They will give you tools to get a better handle on your problem.

Another way to study design patterns is learn their mechanisms and the principles and strategies that underlie them. Learning these will improve your abilities as an analyst and designer. You will know what to do even in situations when a design pattern has not yet been developed, because you will already have the building blocks needed to solve the problem.

In this chapter,

• I describe the open-closed principle, which underlies many design patterns.

• I discuss the principle of designing from context, which was an initial objective of Alexander's patterns.

• I discuss the principle of containing variation.