Iterative Model

In Iterative model, it erative 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.

An iterative life cycle model does not attempt to start with a full specification of
requirements. Instead, development begins by specifying and implementing just part of
the software, which is then reviewed in order to identify further requirements. This process is then repeated, producing a new version of the software at the end of each
iteration of the model.
Iterative Model design
Iterative process starts with a simple implementation of a subset of the software
requirements and iteratively enhances the evolving versions until the full system is implemented. At each iteration, design modifications are made and new functional capabilities are added. The basic idea behind this method is to develop a system through repeated cycles (iterative) and in smaller portions at a time (incremental).

Following is the pictorial representation of Iterative and Incremental model:

Iterative and Incremental development is a combination of both iterative
design or iterative method and incremental build model for development. "During software development, more than one iteration of the software development cycle may be in progress at the same time." and "This process may be described as an
"evolutionary acquisition" or "incremental build" approach."

In incremental model the whole requirement is divided into various builds. During each iteration, the development module goes through the requirements, design, implementation and testing phases. Each subsequent release of the module adds function to the previous release. The process continues till the complete system is ready as per the requirement.

The key to 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. As the software evolves through successive cycles, tests have to be repeated and extended to verify each version of the software.



Iterative Model Application
Like other SDLC models, Iterative and incremental development has some specific
applications in the software industry. This model is most often used in the following
scenarios:


• Requirements of the complete system are clearly defined and understood.

• Major requirements must be defined; however, some functionalities or requested
enhancements may evolve with time.

• There is a time to the market constraint.

• A new technology is being used and is being learnt by the development team
while working on the project.

• Resources with needed skill set are not available and are planned to be used on
contract basis for specific iterations.

• There are some high risk features and goals which may change in the future.


Iterative Model Pros and Cons
The advantage of this model is that there is a working model of the system at a very
early stage of development which makes it easier to find functional or design flaws. Finding issues at an early stage of development enables to take corrective measures in a limited budget.

The disadvantage with this SDLC model is that it is applicable only to large and bulky software development projects. This is because it is hard to break a small software system into further small serviceable increments/modules.

The following table lists out the pros and cons of Iterative and Incremental SDLC Model: