Incremental Model

Diagram : 1

Diagram : 2

Understanding
You can consider the incremental model as multi-waterfall-model of software testing. The whole incremental process is divided into the various number of cycles. Each increment adds additional functionality to the software. An increment includes three cycles: software designing and development, testing, and implementation. Using this model it’s possible to simultaneously develop different product version. For example, you can have the first version in the testing phase, the second one is in the development phase and the third one in the designing phase. This continues until the project is finished.
The advantages it has over other models is that it’s more flexible and it’s cheaper to change the requirements. Also, the software testing process is more effective since it’s easier to test and debug if you use smaller iterations. But the disadvantage is that its costlier when compared to the waterfall model.
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In Incremental Model, each module passes through the requirements, design, implementation and testing phases. A working version of software is produced during the first module, so you have working software early on during the software life cycle. Each subsequent release of the module adds function to the previous release. The process continues till the complete system is achieved.

In the diagram above when we work incrementally we are adding piece by piece but expect that each piece is fully finished. Thus keep on adding the pieces until it’s complete. As in the image above a person has thought of the application. Then he started building it and in the first iteration the first module of the application or product is totally ready and can be demoed to the customers. Likewise in the second iteration the other module is ready and integrated with the first module. Similarly, in the third iteration the whole product is ready and integrated. Hence, the product got ready step by step.

Advantages of Incremental model:-

Generates working software quickly and early during the software life cycle.

This model is more flexible – less costly to change scope and requirements.

It is easier to test and debug during a smaller iteration.

In this model customer can respond to each built.

Lowers initial delivery cost.

Easier to manage risk because risky pieces are identified and handled during it’d iteration.

Disadvantages of Incremental model:-

Needs good planning and design.

Needs a clear and complete definition of the whole system before it can be broken down and built incrementally.

Total cost is higher than waterfall.

When to use the Incremental model:-

This model can be used when the requirements of the complete system are clearly defined and understood.

Major requirements must be defined; however, some details can evolve with time.

There is a need to get a product to the market early.

A new technology is being used.

Resources with needed skill set are not available.

There are some high risk features and goals.