A design pattern in architecture and computer science is a formal way of documenting a solution
to a design problem in a particular field of expertise. The idea was introduced by the
architect Christopher Alexander in the field of architecture and has been adapted for various
other disciplines, including computer science. An organized collection of design patterns
that relate to a particular field is called a pattern language.
The elements of this language are entities called patterns. Each pattern describes a
problem that occurs over and over again in our environment, and then describes the core
of the solution to that problem, in such a way that you can use this solution a million
times over, without ever doing it the same way twice. — Christopher Alexander
The usefulness of speaking of patterns is to have a common terminology for discussing
the situations designers already see over and over.
Overview A pattern must explain why a particular situation
causes problems, and why the proposed solution is considered a good one. Christopher Alexander
describes common design problems as arising from "conflicting forces"—such as the conflict
between wanting a room to be sunny and wanting it not to overheat on summer afternoons. A
pattern would not tell the designer how many windows to put in the room; instead, it would
propose a set of values to guide the designer toward a decision that is best for their particular
application. Alexander, for example, suggests that enough windows should be included to
direct light all around the room. He considers this a good solution because he believes it
increases the enjoyment of the room by its occupants. Other authors might come to different
conclusions, if they place higher value on heating costs, or material costs. These values,
used by the pattern's author to determine which solution is "best", must also be documented
within the pattern. A pattern must also explain when it is applicable.
Since two houses may be very different from one another, a design pattern for houses must
be broad enough to apply to both of them, but not so vague that it doesn't help the
designer make decisions. The range of situations in which a pattern can be used is called its
context. Some examples might be "all houses", "all two-story houses", or "all places where
people spend time". The context must be documented within the pattern.
For instance, in Christopher Alexander's work, bus stops and waiting rooms in a surgery center
are both part of the context for the pattern "A PLACE TO WAIT".
Domain-specific articles Pattern, a way of capturing and communicating
design ideas in architecture. Software design pattern, a standard solution
to common problems in software design. Architectural pattern, a standard solution
to architectural problems in software engineering. Interaction design pattern, used in interaction
design / HCI.
Pedagogical patterns, documenting good practices in teaching.
See also Design Patterns
Style guide, repeatable graphic design elements and styles.
Design paradigm Software design pattern
Anti-pattern a counterpart term, referring to a common situation that creates problems
Further reading Alexander, Christopher. A Pattern Language:
Towns, Buildings, Construction. Oxford University Press. ISBN 0-19-501919-9.
Erl, Thomas. SOA Design Patterns. New York: Prentice Hall/PearsonPTR. p. 864. ISBN 0-13-613516-1.
Frank Buschmann, Kevlin Henney, Douglas C. Schmidt "On Patterns and Pattern Languages"
Gamma, Helm, Johnson & Vlissides. Design Patterns. Addison-Wesley. ISBN 0-201-63361-2.
Jenifer Tidwell. Designing Interfaces Wolfgang Pree. Design Patterns for Object-Oriented
Software Development References
External links Java Design Patterns Full Tutorial
Full collection of design patterns in C++ by Antonio Gulli
Design Patterns in Javascript by Tomás Corral