3.2 Iterative Models
Iterative models are an outgrowth of the traditional waterfall model, with each iteration
incorporating all the stages of the waterfall model in a smaller time-frame, and each
subsequent iteration building on the previous iteration in terms of incorporating more and
more requirements incrementally.
For example, in classical waterfall model, a year long project would have been broken
down into four broad stages of 3 months each in the form of requirements study and
synthesis, analysis and design, development / unit testing / integration testing, and
deployment / rollout. In the iterative model, the same project can be broken down into
three iterations, with each iteration having each of the above four stages, but only one
month in duration as opposed to three. This would allow for the product managers /
business analysts to showcase the product / system to customers / users after the first
iteration, and incorporate their feedback into the next iteration.
Frequently, ideas evolve over time, and so do customer requirements. A perennial
complaint engineers have is that users don‘t know what they want, and to some extent,
this is true. Once the users can touch and feel a system by using it, they get clearer on
what they exactly want, and what more they need in terms of product / system features.
The iterative approach allows for that.
Further, in the hypercompetitive world of product development, product companies are
always under market pressure to bring the product to market yesterday, not a year from
now. Using an iterative approach allows for three to four major product releases a year,
as opposed to just one product release a year, which the traditional waterfall model would
allow for.
Consequently, software engineering should embrace iterative product development as a
minimum competitive requirement, and software estimation techniques should be based
on iterative product development, and its associated techniques: rapid prototyping, agile
methods, and extreme programming.
Below are detailed two such models, the iterative model in the form of a growing spiral,
and the rapid prototyping as a required practice within the first iteration.
