The document discusses three software development models: the Waterfall model, the Spiral model, and the Incremental model. The Waterfall model is a linear sequential process where each phase must be completed before the next begins. The Spiral model is an iterative process combining prototyping and waterfall elements. Each cycle determines requirements and manages risks. The Incremental model is an iterative enhancement of the waterfall model where the project is developed in small increments with each phase producing an increment.

1. System Designs
The Waterfall Model
Spiral model
Incremental Model

2. The Waterfall Model
• The Waterfall Model was first Process Model to be
introduced. It is also referred to as a linear-sequential
life cycle model. In a waterfall model, each phase must
be completed fully before the next phase can begin. At
the end of each phase, a review takes place to
determine if the project is on the right path and whether
or not to continue or discard the project. In this
model software testing starts only after the
development is complete.

3. Advantages of waterfall model
• This model is simple and easy to understand and use.
• It is easy to manage due to the rigidity of the model.
• Each phase has specific deliverables and a review process.
• Phases do not overlap.
• Waterfall model works well for smaller projects where
requirements are very well understood.

4. Disadvantages of waterfall model
• It is very difficult to go back and change something
that was not well-thought out in the concept stage.
• No working software is produced until late during
the life cycle.
• Not a good model for complex and object-oriented
projects.
• Poor model for long and ongoing projects.

5. Water Fall Model Diagram

6. Spiral model
• In the 1980s; Boehm introduced a process model known as the spiral
model. IEEE defines the spiral model as 'a model of the software
development process in which the constituent activities, typical
requirements analysis, preliminary and detailed· design, coding,
integration, and testing, are performed iteratively until the software is
complete. The spiral model comprises activities organized in a spiral,
and has many cycles. This model combines the features of the
prototyping model and waterfall model and is advantageous for large,
complex, and expensive projects. It determines requirements problems
in developing the prototypes. In addition, it guides and measures the
need of risk management in each cycle of the spiral model.

7. Advantages of Spiral Model
• Avoids the problems resulting in risk-driven approach in the
software.
• Specifies a mechanism for software quality assurance
activities.
• Is utilized by complex and dynamic projects.
• Re-evaluation after each step allows changes in user
perspectives, technology advances, or financial perspectives.
• Estimation of budget and schedule gets realistic as the work
progresses.

8. Disadvantages of Spiral Model
• Assessment of project risks and its resolution is not an easy
task.
• Difficult to estimate budget and schedule in the beginning.

9. Spiral Model Diagram

10. Incremental Model
• The incremental model (also known as iterative enhancement
model) comprises the features of waterfall model in an iterative
manner. The incremental model has phases similar to the linear
sequential model. During the implementation phase, the project
is divided into small subsets known as increments that are
implemented individually. This model comprises several phases
where each phase produces an increment. These increments are
identified in the beginning of the development process and the
entire process from requirements gathering to delivery of the
product is carried out for each increment.

11. Advantages of Incremental Model
• Avoids the problems resulting in risk driven approach in
the software.
• Understanding increases through successive refinements.
• Performs cost-benefit analysis before enhancing software
with capabilities
• Incrementally grows in effective solution after every
iteration
• Does not involve high complexity rate
• Implementation occurs rapidly for a small subset of the
software.

12. Disadvantages of Incremental Model
• Requires planning at the management and technical level.
• Becomes invalid when there is time constraint on the
project schedule or when the users cannot accept the
phased deliverables

13. Incremental Model Diagram