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Spiral Model

  • Spiral model is an evolutionary software model.
  • Spiral model may be viewed as a Meta model, because it can accommodate any process model.
  • Spiral model focuses on identifying and eliminating high risk problems.

Following is the illustration of Spiral model:

  • First Quadrant :It determine the objective and alternative solution possible for the phase under consideration.
  • Second Quadrant: We evaluate different alternatives based on objective and constraint. To resolve risk.
  • Third Quadrant: It emphasises development of strategies to resolve the uncertainties and risks.
  • Fourth Quadrant: We determine the objective that should be full filled in next cycle to get complete system.

Characteristics of Spiral Model:

  • It is cyclic not linear like Waterfall model.
  • Each cycle of Spiral Model consist of four stages.
  • Each stage is represented by quadrant of Cartesian Diagram.
  • Radius of Spiral represent cost accumulated so far in the process.
  • Angular dimension represent progress in process.

Advantages of Spiral Model:

  • It is risk driven model.
  • It is very flexible.
  • Less documentation is needed.
  • It uses prototyping.
  • It is more realistic model for software development.

Disadvantages of Spiral Model:

  • Not suitable for small projects.
  • Cost is very high.
  • Rely on risk assessment expertise.
  • Excellent management skills needed.
  • Involvement of different persons makes it complex too.

Limitations of Spiral Model:

  • Software development has no strict standard.
  • Particular phase has no particular beginning and end.

When to use Spiral Model:

  • Spiral model is used when experimenting on technology.
  • When trying out new skills.
  • When the user is not able to offer requirements in clear terms.
  • When system is very complex with lot of functions  and facilities.
  • When requirements is not clear.
  • When the intended solution has multi user, multi functions, multi features, multi locations applications to be used on multiple platforms.