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The first model we want to discuss is the grandfather of

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all life cycle models. And it is the waterfall model. In

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the waterfall model the project progresses to an orderly sequence of

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steps. From the initial software concept, down until the final phase.

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Which is system testing. And at the end of each phase

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there will be a review to determine whether the project is

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ready to advance to the next phase. The pure waterfall model

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performs well for softer products in which there is a stable

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product definition. The domain is well known and the technologies

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involved are well understood. In these kind of domains, the

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waterfall model helps you to find errors in the early,

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local stages of the projects. If you remember what we discussed,

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this is the place where we want to find errors,

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not down here because finding them here will reduce the cost

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of our overall software development. The main advantage of the

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waterfall model is that it allows you to find errors early.

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However, the main disadvantages of the waterfall model arise

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from the fact that it is not flexible. Normally,

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it is difficult to fully specify requirements at the

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beginning of a project. And this lack of flexibility is

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far from ideal when dealing with project in which

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requirements change, the developers are not domain experts or

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the technology used are new and evolving, that is

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it is less than ideal for most real world projects.