Software Models- Spiral Model

Every one of us usually think that there is no need of developing model or make pre-plan before developing software but in reality making software life cycle model is the key ingredient for a successful software,as it encourages development of software in a systematic and disciplined manner, it also help other programmers to easily understand the exact working of software.

Spiral model is one of the software life cycle models. As it's name implies it consist of numbers of loops which basically shows phases of software process. Over every loop one or more features are elaborated and analyzed and the risks at that point are identified and removed by making prototype model. So the risk of failure is removed at every phase.

Phases of the Spiral Model
Each phase in model is divided into four quad..

•  In first quad, some features of product are identified and they became objective of this phase. the objectives are investigated,elaborated and analyzed so as to obtain risks associated with that phase. also alternative solution possible for the phase are proposed. 

• In second quad, the solutions are evaluated and best solution is selected by making appropriate prototype.

•  third quad, consist of  developing  and verifying next level of product.

• Last quad, concern with reviewing result with the required and planning next iteration around spiral.

The radius around spiral at any point would represent the cost incurred in the project so far,qnd angular dimension would represent the progress made so far in the current phase.
this model is also called as "meta model" as it subsumes all other models.