What are Patterns?

Table of Contents

The following contains a tentative definition of what we are looking for in the pilot study and what we should record when we find it.

What is a design pattern?

A Pattern Template

The following is a design-pattern template in the the Gang of Four style. We may want to consider using it to documenting what we find.
Pattern Name (Scope, Purpose)
The pattern's name conveys the essence of the pattern succinctly. A good name is vital, because it will become part of your design vocabulary.
A short statement that answers the following questions: What does the design pattern do? What is its rationale and intent? What particular design issue or problem does it address?
Also Known As
Other well-known names for the pattern, if any.
A scenario that illustrates a design problem and how the class and object structures in the pattern solve the problem. The scenario will help you understand the more abstract description of the pattern that follows.
What are the situations in which the design pattern can be applied? What are examples of poor designs that the pattern can address? How can you recognize these situations?
The classes and/or objects participating in the design pattern and their responsibilities.
How the participants collaborate to carry out their responsibilities.
How does the pattern support its objectives? What are the trade-offs and results of using the pattern? What aspect of system structure does it let you vary independently?
What pitfalls, hints, or techniques should you be aware of when implementing the pattern? Are there language-specific issues?
Sample Code and Usage
Code fragments that illustrate how you might implement the pattern in C++ or Smalltalk.
Known Uses
Examples of the pattern found in real systems. We include at least two examples from different domains.
Related Patterns
What design patterns are closely related to this one? What are the important differences? With which other patterns should this one be used?

This page last modified on 11 November 1997.