Describe spiral model with its advantages and disadvantages.

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Spiral Model

- The spiral model, also known as the spiral lifecycle model or Boehm's model was introduced by Barry Boehm in 1988. It is a system development model based on process iteration. 

- This model of development combines the features of the prototyping model and the waterfall model in order to eliminate almost every possible/ known risk factor from it. 

- This model follows a spiral process as the development of the software takes place. 

- In this model, the development of each modified version of the system prototype is carefully designed using the steps of the waterfall model. 

- Starting from the center of the spiral process, and moving outward in the spiral route, each iteration helps to build a more complete version of the system in a progressive manner. 

- The spiral model is similar to the incremental model, with more emphasis placed on risk analysis.

 

# The spiral model has the following major phases:



1. Customer Communication: In this step, effective communication is established between developer and customer to identify the customer requirements.

2. Planning: In this phase, the objectives, alternatives, and constraints of the projects are determined and are documented. The objectives and other specifications are fixed in order to decide which strategies to follow during the project life cycle.

3. Risk analysis: This is the most important phase of the spiral model in this phase all possible alternatives, which can help in developing a cost effective project are analyzed and strategies are decided to use them. This phase has been added especially in order to identify and resolve all the possible risks in the project development. A prototype is produced at the end of the risk analysis phase to proceed with available data.

4. Engineering: In this phase, the actual development of the project is carried out. The output of this phase is passed through all the phases iteratively in order to obtain improvements in the same. 

5. Construction and release: Tasks required constructing, testing, installing, and providing user support (e.g., documentation and training).

6. Customer evaluation: In this phase, the developed product is passed onto the customer in order to receive customer comments and suggestions which can help in identifying and resolving potential in the developed software. This phase is much similar to the testing phase. This phase allows the customer to evaluate the output of the project to date before the project continues to the next spiral.


Advantages of Spiral Model

- High amount of risk analysis hence, avoidance of Risk is enhanced.

- Good for large and mission-critical projects.

- Strong approval and documentation control.

- Additional Functionality can be added at a later date.

- Software is produced early in the software life cycle.


Disadvantages of Spiral Model

- Can be a costly model to use.

- Risk analysis requires highly specific expertise.

- Project's success is highly dependent on the risk analysis phase.

- Doesn't work well for smaller projects.


When to use the Spiral model

- When costs and risk evaluation is important It is used for medium to high-risk projects

- When users are unsure of their needs

- When requirements are complex It is used when significant changes are expected (research and exploration)


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