Boehm's spiral model

Spiral process model was proposed by boehm in1988. Spiral model is represented as spiral rather than a sequence of activities, from one activity to another activity. The software process has four phases. The innermost layer concerned with system feasibility. The outermost layer with requirement definition, the next layer with design and so on. Changes are result of project risk and risk management activities are used to reduce risk in the project. Both activity change avoidance and change tolerance are both combine in spiral model. Spiral model combine the feature of waterfall model, incremental model, evolutionary model based on risk patterns.

This model is used in information technology (IT). For large, expensive, and complicated projects the spiral model is suitable.

Spiral model is better than other software model b/c obvious identification of risk. Spiral model is important when requirement are complex and user is unclear of its own needs.

If research and exploration are expected than spiral model is used.

                                              Spiral model

                          Four phases of spiral model

Determine objectives:-

                            In first phase we determine the objective of the user and define the functionality of the software and constrain on functionality or (operation) must define.

Project risks are identified and strategies are plan according to risks detail management plan is drawn.

Identify and resolve risk.

                            In this step project team identify the possible risk in the software, and detail analysis is carried out. Risks reduction techniques are used to resolve the risks in the system. For example requirement are inappropriate than prototype of the system is developed.

Development and testing phase.

                            Design the new system to meet the requirement. Development model is selected. Such as integration of sub system is an identified risk than waterfall model is a best development model to use. And system is passes to testing phase to check that the new system meet the user requirement

Plan the next phase.

                      Individual unit are integrate and test the system as a whole, if system is work according to user requirement  the system is delivered to end user, if not than determine objectives of the user. The preceding steps are repeated until the customer is satisfied that the final product is achieved. Final system is tested thoroughly and routine maintenance is carried to prevent failure.

              Advantages and disadvantages of spiral model

        Advantages:-

   Analysis of risks and avoidance of risk is enhanced.

  Add the additional functionality in the system at the end.

  For Mission critical project spiral model is important.

          Disadvantages:-

High level of experts is required for risk analysis.

  Spiral model is costly.

  Success of the system is dependent on risk analysis phase.