The creation of large software applications is rarely, if ever, a simple and straightforward business. There are all the problems associated with vanilla programming, as also those associated with running a successful business, as well as the need to function in an environment where the competition is always fierce. There is not a great deal of scope for trial and error, and it is necessary to use a well-defined and rigorously enforced process model for software development that would form the basis for the creation of high quality software.

The standard life-cycle model of software is called a "waterfall model," because it is supposed to go down through a series of steps, reminding one of the route a natural waterfall takes over a series of rocks at different levels.

In the traditional waterfall model, the first step in the software life-cycle is requirements analysis--this is the...