Object Oriented Design

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.