Patterns : a look

A pattern is an especially clever and insightful way of solving a particular class of problems. It represents a complete idea within a program, and thus it can sometimes appear at the analysis phase or high-level design phase. It can exist at many levels from very low-level specific solutions to broadly generalized system issues. A patterns cover various ranges of scale and abstraction and are grouped into three categories:
    1. Architectural Pattern
        An architectural pattern expresses a fundamental structural organization schema for software systems. It provides a set of predefined subsystems, specifies their responsibilities, and includes rules and guidelines for organizing the relationships between them.
    2. Design Patterns
        A Design pattern provides a scheme for refining the subsystems or components of a software system, or the relationships between them. It describes a commonly-recurring structure of communication components that solves a general design problem within a particular context.
    3. Idioms
        An idioms is a low-level pattern specific to a programming language. An idiom describes how to implement particular aspects of components or the relationships between them using the features of the given language.

Some useful definitions of Design Patterns have emerged as the literature in this field has expanded.

• “Design patterns are recurring solutions to design problems you see over and over.” (The Smalltalk Companion)
• “Design patterns constitute a set of rules describing how to accomplish certain tasks in the realm of software development.” (Pree 1994)
• “Design patterns focus more on reuse of recurring architectural design themes, while frameworks focus on detailed design and implementation.” (Coplien and Schmidt 1995)
• “A pattern addresses a recurring design problem that arises in specific design situations and presents a solution to it.” (Buschmann et al., 1996)
• “Patterns identify and specify abstractions that are above the level of single classes and instances, or of components.” (Gamma et al., 1993)