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Importance of Design Patterns

Over the last few years, patterns have been gained attention in the software community. The use of patterns has helped solve issues faced while designing and reusing applications and libraries. These patterns capture knowledge from various parts of software developing. But as the number of patterns increases, the need to organize the patterns becomes more important. There should be a strong classification scheme to organize patterns in a library and help users in finding and storing patterns. Developing such a classification scheme involves finding useful criteria that should reflect natural properties of patterns

Buschman et al

According to Buschman, classification is based on three criteria. The functionality criteria classifies patterns based on the specific functionality that the design pattern will be used for. The structural principles classifies patterns based on the architectural patterns that the design pattern is utilizing.

Functionality	Structural Principle
Creation	Abstraction
Communication	Encapsulation
Access	Separation of concerns
Computation of complex tasks	Coupling and cohesion

Patterns which belong to the sub category creation specify the manner in which to instantiate certain complex recursive or aggregate object structures. Patterns belonging to the subcategory communication describes the communication protocol to be followed during the remote or independent development of certain collaborating objects. Patterns of the access category will describe the scope of a particular object. Patterns belonging to the category organizing the computation of complex tasks specify the way in which responsibility can be allocated among collaborating objects.

Patterns belonging to the subcategory abstraction gives an abstract overview of functionality in a software system. Patterns belonging to the subcategory encapsulation hide details of objects to eradicate dependencies.Patterns in the subcategory separation of concern segregates specific responsibilities into different objects or components to solve a particular task or provide a certain service. Patterns belonging to the category coupling and cohesion will ease out the structural and communicational dependencies between strongly coupled objects.

Coad

Coad organizes his pattern classification around a certain pattern which will further serve as a template for other patterns that follow.

Pattern	Description
fundamental pattern	template for other patterns
aggregate patterns	patterns that interact with transaction players
plan patterns	patterns that interact with a plan player
interaction patterns	Patterns which interact with the other players

Pree

Pree classification is based on the structure of the design pattern.

• Basic inheritance and interaction patterns
• Patterns for structuring object-oriented software systems
• Patterns based on recursive structures
• Patterns relying on abstract coupling
• Patterns related to the MVC-framework

Zimmer

Zimmer classification provides a new classification of the GoF design pattern proposed by Gamma et all. Three kinds of relationships are defined and a pattern is categorized based on what relationship it supports.

• X uses Y in its solution

X uses a design pattern Y as part of its solution.

• Variant of X uses Y in its solution

X may or may not utilize Design pattern Y as part of its solution.

• X is similar to Y

X and Y address a similar kind of problem.

Similarities and Differences in the Classification approach

In contrast to the classification by Gamma et. al, a pattern can belong to more than one category per criterion in Buschman et. al classification. Zimmer uses the relationships that Gamma et. al describe in each pattern's "Related Patterns" section. These relationships address a wide range of issues from “the pattern uses another pattern in its solution" to “the pattern is similar to another pattern in constructing object structures". Therefore there are extensive similarities in the classification scheme. Coad neither stress the importance of a classification nor does he describe his organization of patterns in a thorough manner.