1. Iterative Waterfall Model
Lecture-3

2. 3.1 Classical Waterfall Model - Advantages
The waterfall model provides a systematic and sequential approach to software development and is better than the build and fix approach.
It is easy to understand ,implement and easy to administer.
It clearly divides the problem into distinct phases that may be performed independently
A simple and natural approach to solving the problem

3. 3.2 Classical Waterfall Model - Limitations
But, in this model, complete requirements should be available at the time of commencement of the project
But in actual practice, the requirements keep on originating during different phases.
Moreover, it does not incorporate any kind of risk assessment. In waterfall model, a working model of software is not available.
Thus, there is no methods to judge the problems of software in between different phases.
So it is not suitable for the large projects

4. 3.3 Iterative Waterfall Model
This model was developed to remove the shortcomings of waterfall model.
This is also referred as Modified Waterfall Life-Cycle Model
The classical waterfall model is an idealistic model because it assumes that development error is ever committed by the engineers during any phase of life cycle of software development.
But in practical environment of development, engineers do commit large number of errors in almost every phase of life cycle of software development.

5. 3.3 Iterative Waterfall Model Contd
Once defect is detected, the engineers need to go back to the phase where the defects had occurred and redo some work done during that phase and the subsequent phases to correct the defects and its effect on the latter phases.
Therefore a feedback path is needed in the classical waterfall model from every phase to its preceding phase.
The principle of detecting errors as close to their points of introduction as possible is called phase containment error.

6. 3.3 Iterative waterfall model
Feasibility study
Req. Analysis & specification
Design
Coding & Unit Testing
Integration & System Testing
Maintenance

7. 3.3 Iterative waterfall model Contd
In spite of best efforts put to detect errors in the same phase some errors do escape detection and may get noticed in the later phase.
Thus practically several iterations through the waterfall stages are normally necessary to develop the final products.
In this model, the phases of software development remain the same, but the construction and delivery is done in the iterative mode.

8. 3.4 Major Extensions in this model
It introduces iterations between the phases along with the restrictions of providing iterations, if possible, only between successive phases in order to reduce the expense of revision that results from iterations over multiple phases.
Provisions for verification and validation of the phase output in the software lifecycle are added.
Provide overlap and feedback between phases

9. 3.5 Advantages and Disadvantages
It is most widely used software development model
Simple to understand and easy to implement.
Disadvantages
Going back a phase or two can be a costly affair.
Even a small change in any previous stage can cause big problem for subsequent phases as all phases are dependent on each-other.

10. 3.6 When to use Iterative waterfall model?
Suitable only for well-understood problems
Not suitable for very large and risk prone projects
This methodology is preferred in projects where quality is more important as compared to schedule or cost.
In development of database-related software and commercial projects.
In development of E-commerce website or portal.
In development of network protocol software.