★ When the requirements are very clearly know, documented and not subject to change then we can follow the waterfall model.

★ Most of the companies follow the V mode for the development because this model includes both verification and validation activities and testing is involved in earlier phase.

★ Iterative model can be used to build application where requirement changes after a period of times or application features or added on with smaller release. When the client is ready for the delivery of the product in parts or phases.