This process model is characterised
by the recognition of risk factors within software system production. Risks,
being a consequence of inadequate information, are resolved by gathering information
to reduce the level of uncertainty. There are no fixed phases, however each
phase is divided into four stages. Each round of the spiral is equivalent to
one phase of the development process. The Waterfall and Evolutionary models
are subsets of the spiral model.
Before embarking on each phase
a standard form containing eight basic features is completed. The features
The quadrants into
which each phase is divided structure the process as follows :
- Objective setting
The specific objectives of this phase of the project are defined. Constraints
on the process and product are identified and a detailed management plan drawn
up. Project risks are identified. Alternative strategies, depending on these
risks, may be planned.
assessment and reduction
For each identified risk, a detailed analysis is carried out. Steps are taken
to reduce the risk.
One of the standard development models for the system is chosen. This may
be evolutionary prototyping, the waterfall model or formal transformations.
The project is reviewed and a decision made whether to continue with a further
loop of the spiral. If it is decided to continue, plans are drawn up for the
next phase of the project.
Too involved for small scale
Reduces risk factors within the development process. Excellent process
visibility with documentation produced at each quadrant and phase.