Iterative, spiral life cycle model

• During development several iterations are implemented. Each iteration ends with the product release ready to use (try) by end users. The purpose of the iterations is to provide users with result to get the feedback from them as soon as possible.	See enlarged view
• As each release is developed, the activities and tasks in the Development process are employed repeatedly, in serial or parallel, with partial overlapping, in the same sequence for all the releases. The release is completed when all development tasks are completed

•Supporting and Organizational processes are employed in parallel with the Development process.

•Quality related activities are treated as an integral part of the software life cycle and appropriated those activities to relevant processes and the personnel responsible for performing the process.

The rationale

• The requirements are not fully understood and cannot be defined initially: the requirements are partially defined up front, than are refined in each successive release.

Risk of the iterations

Growing participants' requirements changes after each iteration. Each new requirement or change of the requirements must be processed as following:

• Impact on the project scope (schedule and or budget).
• Any impact must be reported to project participants, who make the decision.
• Changes could be rejected, postponed or approved with the changes to project schedule and or budget.