programming A description of an object-oriented design

technique which names, abstracts and identifies aspects of a

design structure that are useful for creating an

object-oriented design. The design pattern identifies

classes and instances, their roles, collaborations and

responsibilities. Each design pattern focuses on a particular

object-oriented design problem or issue. It describes when it

applies, whether it can be applied in the presence of other

design constraints, and the consequences and trade-offs of its

use.