spiral life cycle model in software development[working,advantages & limitations[check here]]

Boehm's Spiral Model

The Spiral Life-cycle  model combines elements of the waterfall model, along with an emphasis on the use of risk management techniques.
Boehm proposed a spiral model (Boehm 1987) where each round of the spiral.

Identifies the sub-problem which has the highest risk associated with it
Find the solution for that problem.

It's feature is that it is primarily risk-avoidance driven rather then document-driven, code driven or release driven.
Spiral Model in software engineering

Working of spiral software development life-cycle model:-

Each cycle of the spiral model uses the same level processes that are outlined as:

  •  Determine objectives, alternatives and constraints.
  • Evaluate alternatives, identify and resolve risks.
  • Develop, verify next level product.
  • Plan next phase.

Within this framework, the tasks may resemble those of the waterfall lifecycle model with the additional of the specific risk management techniques. A review occurs as a project management checkpoint after each cycle is completed.
 The redical dimension of the graph depicts the increasing total cost of the project and the angular dimension depicts progress through steps.

1. Each cycle begins with identification of the objectives of the portion of the project being eleborated on this cycle, the alternative means of implementing this portion of the product and the constraints imposeed on the appplication of the alternatives.
2. The next step is to evaluate the alternative relative to the objectives and constraints.
3. Often, as an outcome of this evaluation, areas of uncertanity may be identified that are significant source of risk. This may include the use of prototyping, simulations, benchmarking and other risk-resolution and techniques.
4. The first risk to be resolved may be one that threatens the planned concept of operations of the new systems.
5. Once the prototype or other risk-resolution techniques is effective in mitigating that risk, the next steps of developing the concept of operation can be taken, followed by the next cycle.
6. The second cycle proceeds to develop the software requirements and to perform requirements validation, again proceeds by planning, determination of objectives, alternatives, and constraints, and risk analysis and mitigation.
7. The third and fourth cycles focus on further stages of developments as shown in the lower quadrant of the figure. and are preceded by planning through risk mitigation relevant to those stages of development.

 At this point, all parties with a vested interest review the results of the previous cycle. While each cycle does not include a develop process,software is not actually developed for release until the final cycle.

Advantages of Spiral Life-cycle Model.

  •  The primary advantage of the spiral model is that it's range of options allows it to accommodate the best features of existing software process models, while it's risk-driven approach helps it to avoid most of the difficulties.
  •  In appropriate situations the spiral model becomes equivalent to one of the existing process models. In other situations ,it provides guidance on the best mix of existing approaches to be applied to a given projects.
  • The spiral model can be used with a spectrum of methodologies whether they are specification-oriented, process-oriented and object-oriented.

Limitations of Spiral Life-cycle model.

  • The lie-cycle steps need further elaboration to assure that participants in software development have a common understanding.
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