#27586
Extreme Programming (or XP) is a popular software development process that encourages a return to the days of little or no documentation, Design After First Testing, and Constant Refactoring After Programming. Despite its popularity, not everyone thinks XP is a good idea.
Software Reality (2005). Articles>Collaboration>Agile>Extreme Documentation
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Functional Specification Standard 
In general terms, the functional specification states what the proposed system is to do, whereas design is how the system is to be constructed to meet the functional specification. However in writing it, some consideration of design issues must take place, to ensure a realistic system is specified.
Software Reality. Articles>Writing>Specifications>Functional Specifications
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Writing a Functional Specification 
A functional specification can substantially simplify and streamline the process of application development. Intended to describe how a piece of software works, it provides a ready reference for software developers andaligns large and disparate development teams to a single goal. In the process, it provides technical clarity on how the different components of aparticular applications are to be designed, implemented and integrated witheach other, and (if used correctly) significantly reduces the time and costcomponent of any development exercise.
Deepa L. Software Reality (2003). Articles>Writing>Specifications>Functional Specifications
