Design pattern (computer science)

In software engineering, design patterns are standard solutions to common problems in software design. Instead of focusing on how individual components work, design patterns take a systematic approach, which focuses on the patterns of interaction. Design patterns describe abstract systems of interaction between classes, objects, and communication flow.

Contents
1 History
2 Uses
3 Classification
4 Documentation
5 Critique
6 Related topics
7 References
8 External links

History

Patterns originated as an architectural concept by Christopher Alexander.

The phrase was introduced to computer science in 1995 by the text Design Patterns: Elements of Reusable Object-Oriented Software. The scope of the term remained a matter of dispute into the next decade. Algorithms are not thought of as design patterns, since they solve computational problems rather than design problems.

Uses

Design patterns can speed up the development process by providing tested, proven development paradigms. Effective software design requires considering issues that may not become visible until later in the implementation. Reusing design patterns helps to prevent subtle issues that can cause major problems.

Often, people only understand how to apply certain software design techniques to certain problems. These techniques are difficult to apply to a broader range of problems. Design patterns provide general solutions, documented in a format that doesn't require specifics that are tied to a particular problem.

Patterns allow developers to communicate with standardized names of design patterns. Common design patterns can be improved over time, making them likely to perform better than ad-hoc designs.

Classification

Design patterns can be classified based on multiple criteria, the most common of which is the basic underlying problem they solve. According to this criterion, design patterns can be classified into various classes, some of which are:

Documentation

The documentation for a design pattern should contain enough information about the problem that the pattern addresses, the context in which it is used, and the suggested solution. Nonetheless, authors use their own layouts to document design patterns, and these layouts usually resemble the essential parts. The authors usually include additional sections to provide more information, and organize the essential parts in different sections, possibly with different names.

A commonly used format is the one used by the Gang of Four. It contains the following sections:

Critique

Some feel that the need for patterns results from using computer languages or techniques with insufficient abstraction ability. Under ideal factoring, a concept should not be copied, but merely referenced. But if something is referenced instead of copied, then there is no "pattern" to label and catalog. It is also said that design patterns encourage navigational database-like structures instead of the allegedly cleaner relational approach where such structures are viewpoints instead of hard-wired into programming code. However, critics of the relational approach suggest that it does not integrate well enough with behavior. The level of coupling that should be supplied between behavior and data is a contentious topic.

Related topics

References

External links

See also: Design pattern (computer science), 16 May, 1988, 1995, 1997, 1998, 2002, 2003, Abstraction, Aggregate pattern