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This is the context in which, typically, a pure

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waterfall process will work well. Why? Well, because it's a

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context in which requirements are usually well understood. The

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domain is well understood, so that kind of system has

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been built many times before. And also, it's a

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system in which we don't expect requirements to change dramatically

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over time. Therefore, a waterfall model, in which we collect

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all the requirements at the beginning and then we move

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to the subsequent phases might be the most appropriate one. Probably

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we don't want to do evolutionary prototyping in the case of

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the control system for an airplane. Same thing holds for TDD,

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so we want to be a little more rigorous in those cases.