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Extreme Programming (XP) is a software engineering methodology, the most prominent of several agile software development methodologies.
Like other agile methodologies, Extreme Programming differs from traditional methodologies primarily in placing a higher value on adaptability than on predictability.
Proponents of XP regard ongoing changes to requirements as a natural, inescapable and desirable aspect of software development projects; they believe that being able to adapt to changing requirements at any point during the project life is a more realistic and better approach than attempting to define all requirements at the beginning of a project and then expending effort to control changes to the requirements.
XP prescribes a set of day-to-day practices for managers and developers; the practices are meant to embody and encourage particular values. Proponents believe that the exercise of these practices—which are traditional software engineering practices taken to so-called "extreme" levels—leads to a development process that is more responsive to customer needs ("agile") than traditional methods, while creating software of better quality
Extreme Programming Explained describes Extreme Programming as being:
An attempt to reconcile humanity and productivity
A mechanism for social change
A path to improvement
A style of development
A software development discipline
The main aim of XP is to reduce the cost of change. In traditional system development methods (like SSADM) the requirements for the system are determined at the beginning of the development project and often fixed from that point on. This means that the cost of changing the requirements at a later stage (a common feature of software engineering projects) will be high.
XP sets out to reduce the cost of change by introducing basic values, principles and practices. By applying XP, a system development project should be more flexible with respect to changes.
Extreme Programming initially recognized four values. A new value was added in the second edition of Extreme Programming Explained. The five values are:
- Communication
- Simplicity
- Feedback
- Courage
- Respect (the latest value)
Building software systems requires communicating system requirements to the developers of the system. In formal software development methodologies, this task is accomplished through documentation.
Extreme Programming techniques can be viewed as methods for rapidly building and disseminating institutional knowledge among members of a development team. The goal is to give all developers a shared view of the system which matches the view held by the users of the system.
To this end, Extreme Programming favors simple designs, common metaphors, collaboration of users and programmers, frequent verbal communication, and feedback.
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