Monday, 23 January 2012

Spiral Model

This article gives the overview about Spiral Model.This is not the first model to be used to for Iteration. But this is the first model to explain why iteration matters in Software or Application Development. Normally iteration takes 6 months to 2.5 years long. Normally each phase starts with the design and ends with the Client. It means that the software or application should meet the requirement of the client. Analysis and Engineering efforts are applied in each phase of the project to keep an eye on achieving the goal.


This model is also called as Spiral Life Cycle Model is a System Development Model which was widely used in the organizations which are big and developing complex and expensive applications. This model is the combination of Prototype and Waterfall model. 


We have the following steps involved in Spiral Model:
01. The requirements of the system to be developed is gathered from the users and defined as much details as possible. We used to gather the user information by interviewing the users by explaining internal and external aspects of the available system or application.
02. A preliminary design is created for the new system.
03. Based on the preliminary design, we will develop the 1st Prototype of the system.This is a scaled down version of the system, which has the approximation of the final product.
04. A Second Prototype of the system is developed by using the following procedures.
      04.0.1. Evaluating the first prototype by means of strengths, weakness and risks.
      04.0.2  Requirements of the second prototype is defined.
      04.0.3  Plan and Design the second prototype.
      04.0.4 Second prototype is developed and tested.
05. 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.
06.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
07.The preceding steps are iterated until the customer is satisfied that the refined prototype represents the final product desired.
08.The final system is constructed, based on the refined prototype.
09.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.
Like other models we have both advantages and disadvantages.

  1. Estimates (i.e. budget, schedule, etc.) become more realistic as work progresses, because important issues are discovered earlier.
  2. It is more able to cope with the (nearly inevitable) changes that software development generally entails.
  3. 03.Software engineers (who can get restless with protracted design processes) can get their hands in and start working on a project earlier
Disadvantages:
    1. Highly customized limiting re-usability
    2. Applied differently for each application.
    3. Risk of not meeting budget or schedule
    4. Risk of not meeting budget or schedule

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