Monday, June 28, 2010

Incremental or Iterative Development

The incremental, or iterative, development model breaks the project into small parts. Each part is subjected to multiple iterations of the waterfall model. At the end of each iteration, a new module is completed or an existing one is improved on, the module is integrated into the structure, and the structure is then tested as a whole.

For example, using the iterative development model, a project can be divided into 12 one- to four-week iterations. The system is tested at the end of each iteration, and the test feedback is immediately incorporated at the end of each test cycle. The time required for successive iterations can be reduced based on the experience gained from past iterations. The system grows by adding new functions during the development portion of each iteration. Each cycle tackles a relatively small set of requirements; therefore, testing evolves as the system evolves. In contrast, in a classic waterfall life cycle, each phase (requirement analysis, system design, and so on) occurs once in the development cycle for the entire set of system requirements.

The main advantage of the iterative development model is that corrective actions can be taken at the end of each iteration. The corrective actions can be changes to the specification because of incorrect interpretation of the requirements, changes to the requirements themselves, and other design or code-related changes based on the system testing conducted at the end of each cycle.

The main disadvantages of the iterative development model are as follows:

  • The communication overhead for the project team is significant, because each iteration involves giving feedback about deliverables, effort, timelines, and so on.
  • It is difficult to freeze requirements, and they may continue to change in later iterations because of increasing customer demands. As a result, more iterations may be added to the project, leading to project delays and cost overruns.
  • The project requires a very efficient change control mechanism to manage changes made to the system during each iteration.

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