Iterative Enhancement model

The iterative enhancement life cycle model removes the limitations of the waterfall model and tries to combine the benefits of both prototyping and the waterfall model. The basic idea is that the software should be developed in increments, where each increment adds some functional capability to the system until the full system is implemented. At each step extensions and design modifications can be made. An advantage of this approach is that it can result in better testing, since testing each increment is likely to be easier than testing entire system like in the waterfall model. Furthermore, as in prototyping, the increment provides feedback to the client, which is useful for determining the final requirements of the system.
In the first step of iterative enhancement model, a simple initial implementation is done for a subset of the overall problem. This subset is the one that contains some of the key aspects of the problem which are easy to understand and implement, and which form a useful and usable system. A project control list is created which contains, in an order, all the tasks that must be performed to obtain the final implementation. This project control list gives an idea of how far the project is at any given step from the final system.

Each step consists of removing the next step from the list. Designing the implementation for the selected task, coding and testing the implementation, and performing an analysis of the partial system obtained after this step and updating the list as a result of the analysis. These three phases are called the design phase, implementation phase and analysis phase. The process is iterated until the project control list is empty, at the time the final implementation of the system will be available. The process involved in iterative enhancement model is shown in the figure below.
The project control list guides the iteration steps and keeps track of all tasks that must be done. The tasks in the list can include redesign of defective components found during analysis. Each entry in that list is a task that should be performed in one step of the iterative enhancement process, and should be simple enough to be completely understood. Selecting tasks in this manner will minimize the chances of errors and reduce the redesign work.