Extreme Programming is a software development methodology that is intended to improve software quality and responsiveness to changing customer requirements. As a type of Agile software development, it advocates frequent releases and shorter development cycles, which are intended to improve productivity and introduce checkpoints where new customer requirements can be adopted. Other elements of XP include programming in pairs or doing extensive code reviews, unit testing all of the code and avoiding programming of features until they are actually needed. XP has a flat management structure with simplicity and clarity in code, and a general expectation that customer requirements will change as time passes. The problem domain will not be understood until a later point, and frequent communication with the customer will be required at all times.
Extreme Programming takes its name from the idea that the beneficial elements of traditional software engineering practices are taken to extreme levels. As an example, code reviews are considered a beneficial practice. Taken to the extreme, code can be reviewed continuously with the practice of pair programming.
XP was created by Kent Beck during his work at the struggling Chrysler Comprehensive Compensation System payroll project, or C3, as it was known. In 1996, Chrysler called in Kent Beck as an external consultant to help with its struggling C3 project. The project was designed to aggregate a number of disparate payroll systems into a single application.
Initially, Chrysler attempted to implement a solution, but it failed because of the complexity surrounding the rules and integration. From this point of crisis, Kent Beck and his team took over, effectively starting the project from scratch. The classic Waterfall development approach had failed, so something drastic was required. In Kent Beck’s own words, he just made the whole thing up in two weeks with a marker in his hand and a white board. Fundamentally, the C3 team focused on the business value the customer wanted, and discarded anything that did not work towards that goal. Extreme Programming was created by developers for developers.
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The XP team at Chrysler was able to deliver its first working system within a year. In 1997, the first 10,000 employees were paid from the new C3 system. Development continued over the next year, with new functionality being added through smaller releases. Eventually, the project was cancelled because the prime contractor changed, and the focus of Chrysler shifted away from C3. When the dust settled, the eight-member development team had built a system with 2,000 classes and 30,000 methods. Refined and tested, XP was now ready for the wider development community.
