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## The Software Life Cycle

- The waterfall model did not work.
  - It was difficult to come up with a perfect requirement specification.
  - It was common to discover in the design phase that the requirements were not consistent and needed changing.
  - When a design was implemented, the resulting program might not be fast as desired.
  - When the program was tested, many bugs were found that would best be fixed by reimplementing, or maybe even redesigning.
  - Customers might be unhappy with the finished product.
- A mechanism is needed to deal with unresolved problems from the preceding phase.

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