Extreme programming explained: embrace change
Extreme programming explained: embrace change
Communications of the ACM
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Software describes an imagined machine. To be software, the description must be executable, which means written so a computer can animate it. Non-executable descriptions (specifications, designs, &c.) are instrumental to this work; they are intermediate texts. We advance a model of software development as the collaborative writing of a series of descriptions. We propose the chief distinction of agile development to be the exclusion from this process of the human translation of intermediate texts. We distinguish supported and unsupported communication. We analyse the success of Extreme Programming in terms of avoiding unsupported communication and prioritising feedback from executable descriptions. We describe functional programming techniques to construct notations that allow programmers and users to collaborate writing executable system descriptions, collapsing distinctions between analysis, design, coding and testing. We describe a metric of code clarity, semantic density, which has been essential to the success of this work. We report the use of these techniques in the Pensions division of Britain's largest insurer, and its effect on the business.