spiral model

spiral model

The spiral model is a software development process combining elements of both design and prototyping-in-stages, in an effort to combine advantages of top-down and bottom-up concepts. Also known as the spiral lifecycle model, it is a systems development method (SDM) used in information technology (IT). This model of development combines the features of the prototyping model and the waterfall model. The spiral model is intended for large, expensive and

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Spiral model (Boehm, 1988).

The Spiral Model

The steps in the spiral model can be generalized as follows:

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.

Applications

The spiral model is used most often in large projects. For smaller projects, the concept of agile software development is becoming a viable alternative. The US military has adopted the spiral model for its Future Combat Systems program.

Advantages

The spiral model promotes quality assurance through prototyping at each stage in systems development.