Process Models

Process Models
1-Waterfall model
The waterfall model is an established approach that dominated software development
for a number of years and is widely used. It has the virtue of simplicity.


The principles of the waterfall model are:
it is a series of steps (like a factory production line)
each step is well defined
each step creates a definite product (in some cases a piece of paper)
each product forms the basis for the next step
the correctness of each step can be checked (verification or validation).
The waterfall model gets its name because each stage produces a product, like a
stream of water which passes on to the next stage. So the complete development
process is like a series of small waterfalls – see Figure 21.1. Just as water cannot flow up
a waterfall, information does not flow backwards in the waterfall model. Once a step is
complete, there is no going back.


2-Spiral model
The main feature of the spiral model is the recognition that there is often enormous
uncertainty at many stages during a software development project. It therefore incor-
porates periodic risk assessment. These assessments are followed by identifying alterna-
tive actions, selection of the best action and re-planning.