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IncrementalDevelopment

copying a bit about incremental requirements from my blog...

The great thing about agile projects, is that you don't have to have ALL the requirements up-front, just enough to get started. Once you see the software working (minimally), you can change your mind about the requirements that are not yet implemented or have been implemented.

Consider a non-XP project, one that is not incrementally implementing features. If the customer decides in the middle of the project to change some requirements, the project may have to throw away lots of partially-completed code.

In the middle of an XP project, a requirement is either implemented or not -- the only time a requirement may be partially implemented is during the two-week iteration it was schedule for. Any requirements that haven't been implemented yet can be changed at zero cost. A change for requirements that have already been implemented is essentially the same as adding a new requirement -- it will cost something to be re-implement, and an equivalent amount of other non-implemented requirements should be dropped to keep the project on schedule.

KeithRay 2003.04.05