Iterative Enhancement Models

The iterative process starts with a simple implementation of a small set of the software requirements and iteratively enhances the evolving versions until the complete system is implemented and ready to be deployed. During each iteration, the development module goes through the requirements, design, implementation and testing phases. The process continues till the complete system is ready as per the requirement.

The key to a successful use of an iterative software development lifecycle is rigorous validation of requirements, and verification & testing of each version of the software against those requirements within each cycle of the model.

Working:

This model has the same phases as the waterfall model, but with fewer restrictions. Generally the phases occur in the same order as in the waterfall model, but they may be conducted in several cycles. A Usable product is released at the end of each cycle, with each release providing additional functionality. Customers and developers specify as many requirements as possible and prepare a SRS document. Developers and customers then prioritize these requirements Developers implement the specified requirements in one or more cycles of design, implementation and test based on the defined priorities. 

Advantages:

• Results are obtained early and periodically.
• Parallel development can be planned.
• Progress can be measured.
• Less costly to change the scope/requirements.

Disadvantages:

• Not suitable for smaller projects.
• Management complexity is more.
• End of project may not be known which is a risk.
• More resources may be required.