Patterns

By,

Puja Gajul

Roll No = 26

• The Term ‘Pattern’ The usage of the term ‘pattern’ in software development was inspired by the notion of architectural patterns introduced by Christopher Alexander (ALEXANDER et al. 1977).

• for the design phase and the analysis phase, and idioms for the implementation phase were developed. RIEHLE and ZÜLLIGHOVEN (1996) give a general definition of patterns: ‘A pattern is the abstraction from a concrete form which keeps recurring in specific non-arbitrary contexts.’ defines in reference to analysis patterns.

Types of Patterns in Object-Oriented Software Development

1 )Anti-Patterns :

Unlike other patterns that offer well-proven solutions to recurrent problems, anti-patterns describe negative examples of solutions: they describe behaviour that has been repeatedly observed in practice and its negative effects and point the way to better solutions. Awareness of anti-patterns helps to avoid their negative effects. Anti-patterns can be found in the whole process of software development: in project management, analysis, architecture, design and programming.

2)Requirements Patterns :

Requirements patterns support the creation of the requirements specifications. They specify generic behaviourof systems on a high level of abstraction and thereby help to reach precise and better requirements descriptions for a system more quickly. Requirement patterns are not the

subject of this report to any great extent.

3)Analysis Patterns:

Analysis patterns support the creation of the conceptual model of an application. An analysis pattern provides a re-usable, well-proven model representation of a recurrent subproblem. Thus, analysis patterns facilitate the proper transformation of a concrete problem into an analysis model

4)Architecture Patterns:

Software architecture patterns describe basic organisational principles for designing the structure of a software system. They support the choice of an appropriate software architecture by providing tried and tested solutions for structural and organisational issues. A software architecture pattern contains best practise solutions for decomposing a software system into sub-systems and describes the responsibilities and relationships between the sub-systems

5)Design Patterns :

Design patterns support the creation of the design model. They provide solutions for recurring problems that occur during the transition from the analysis model to the design model (Fig. 1.4). As distinct from analysis patterns which are closely related to a concrete subproblem, design patterns contain more generic model fragments which are dedicated to rather technical or implementationrelatedissues. Similar to analysis patterns, design patterns require some modification when being integrated into the design model at hand

• Terminology :

In the remainder, some technical terms relating to object-oriented patterns are used. These are explained below.

1)Pattern Language – a pattern language is a collection of interrelated patterns for solving a particular problem. The patterns are organisedthrough their relationships within the pattern language.

2)Pattern Template – a pattern template is a template for the description of patterns. A template determines a list of characteristics that have to be more closely defined in order to describe a pattern.

3) Pattern Instantiation – pattern instantiation means the adaptation of a pattern to the concrete problem that is to be solved. Class names, class attributes and class operations are adapted and parts of the pattern that might no longer be needed are omitted.

4) Ad Hoc Modelling – ad hoc modelling or manual modelling means the building of a model without pattern support.

5)Framework – the term ‘framework’ is used in the sense of conceptual framework. Conceptual frameworks are used in science to describe possible approaches to complex problems

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