SPIRAL METHOD

SPIRAL METHOD

What is Spiral Method ? -The spiral model is a risk-driven process model generator for software projects. Based on the unique risk patterns of a given project, the spiral model guides a team to adopt elements of one or more process models, such as incremental, waterfall, or evolutionary prototyping. Spiral Model is a combination of a waterfall model and iterative model. The development team in Spiral-SDLC model starts with a small set of requirement and goes through each development phase for those set of requirements.

History -This model was first described by Barry Boehm in his 1986 paper "A Spiral Model of Software Development and Enhancement". In 1988 Boehm published a similar paper to a wider audience. These papers introduce a diagram that has been reproduced in many subsequent publications discussing the spiral model.

These early papers use the term "process model" to refer to the spiral model as well as to incremental, waterfall, prototyping, and other approaches. However, the spiral model's characteristic risk-driven blending of other process models' features is already present:

[R]isk-driven subsetting of the spiral model steps allows the model to accommodate any appropriate mixture of a specification-oriented, prototype-oriented, simulation-oriented, automatic transformation-oriented, or other approach to software development.

In later publications, Boehm describes the spiral model as a "process model generator", where choices based on a project's risks generate an appropriate process model for the project. Thus, the incremental, waterfall, prototyping, and other process models are special cases of the spiral model that fit the risk patterns of certain projects.

Why is Spiral Model called a meta model ?

The spiral model is called a meta model since it encompasses all other life cycle models. Risk handling is inherently built into this model. The spiral model is suitable for development of technically challenging software products that are prone to several kinds of risks.

There are steps in generalizing spiral method:

1. The new system requirements are defined in as much detail as possible. This usually involves interviewing a number of users representing all the external or internal users and other aspects of the existing system.

2.A preliminary design is created for the new system.

3. A first prototype of the new system is constructed from the preliminary design. This is usually a scaled-down system, and represents an approximation of the characteristics of the final product.

4. A second prototype is evolved by a fourfold procedure: (1) evaluating the first prototype in terms of its strengths, weaknesses, and risks; (2) defining the requirements of the second prototype; (3) planning and designing the second prototype; (4) constructing and testing the second prototype.

5. At the customer's option, the entire project can be aborted if the risk is deemed too great. Risk factors might involve development cost overruns, operating-cost miscalculation, or any other factor that could, in the customer's judgment, result in a less-than-satisfactory final product.

6. The existing prototype is evaluated in the same manner as was the previous prototype, and, if necessary, another prototype is developed from it according to the fourfold procedure outlined above.

7. The preceding steps are iterated until the customer is satisfied that the refined prototype represents the final product desired.

8. The final system is constructed, based on the refined prototype.

9. The final system is thoroughly evaluated and tested. Routine maintenance is carried out on a continuing basis to prevent large-scale failures and to minimize downtime.

Advantage:

1. Additional functionality or changes can be done at a later stage.

2. Cost estimation becomes easy as the prototype building is done in small fragments

3. Continuous or repeated development helps in risk management

4. Development is fast and features are added in a systematic way

5. There is always a space for customer feedback

Disadvantage:

1. Risk of not meeting the schedule or budget

2. It works best for large projects only also demands risk assessment expertise

3. For its smooth operation spiral model protocol needs to be followed strictly

4. Documentation is more as it has intermediate phases

5. It is not advisable for smaller project, it might cost them a lot

Conclusion:

The implementation of this model requires experienced resources as risk analysis is a very integral part of this model and risk analysis requires expertise and as result this model becomes costly. This model is convenient to use for larger projects where you can develop and deliver smaller prototypes and can enhance it to make tha larger software. The four activities (Planning, Risk Analysis, Engineering, and Evaluation) form the intermediary phases of a spiral model and is repeated again for each loop. Each spiral can be termed as loop and each loop is separate development process in a spiral model.

*RESEARCHERS:

ROMANO, JOANNA T.

SOBIGA, TRISHA F.

SALIPOT, ALJOHN M.