Spiral Model

Introduction to Spiral Model

The spiral model is based on the evolutionary approach, proposed by Boehm. This model attempts to use the   linear, sequential and stepwise procedure of linear sequential model and also incorporates the prototyping as needed. Spiral model is shown in fig2.12. This model is represented in the form of spirals where each spiral is connected to another spiral to represent the various phases. Additionally each iteration in the spiral   showed a phase of the software   process.

The process begins at the center of the spiral in clockwise direction. That why the innermost loop represents the system concept. Then next loop represents the development loop and so on. So there are total of four loops or spirals.

1. Product concept: does the feasibility study and produces the product specification.

2. Product development:  develops the software according to the mentioned specification.

3. Product testing: includes the testing of product.

4. Product maintenance; maintains the product where the changes can be done   in the controlled manner.

Each box. Mentioned at the end of every spiral, represents the starting point of another spiral like in the concept development the loop goes iteratively until it is completed. When this phase produces an end product of this phase then the next spiral is started.

Additionally a spiral model is partitioned into six task regions given below:

1. Customer Communication

2. Planning

3. Risk Analysis

4. Engineering

5. Construction and Delivery

6. Customer Evaluation 

1. Customer communication

A meeting is conducted between customer and developer to have an effective and successful discussion.

2. Planning:

After this communication, software planning is done by the developer to include some crucial point slice schedule, cost resources, quality and configuration management and risk to follow the aim and requirements   mentioned by the customer.

3. Risk Analysis

It is the most important region of this model. A risk analyst is chosen to handle all the risks which rise at any time. So the has to manage both technical and managerial risks.  For example if there is a risk that the requirements are inappropriate, then a prototype system may be developed

4. Engineering

This task region is used when one or more representations are built of that software and the best one is to be chosen.

5. Consturction and Release

This task region is required to construct, test install and provide user support.

6. Customer evaluation

In this task region the customer will evaluate the product, checks its various steps and then may give its feedback to the developer.

These were the various task regions of the spiral model. Next the most important point in spiral model is that this model includes a very important phase of risk analysis.  Any raised risks should be handled regularly   time to time. For example, if we need much human resources and in between the project development some staff members leave the project. Then the human resources risk will become high and it must be handled immediately by the risk analyst. Some other example of risk.

  • During a long development, the user requirement is neglected.
  • A competition has come up with same project.
  • The modules are not completed within the specified time.
  • Software performs too slowly.
  • Software needs much memory.
  • New software development books become unavailable.
  • User requirements were misunderstood.
  • The user changes one of the requirements.
  • So risk minimisation is a very important project management activity.


1. The software development indicates that the software remain active till it is retired.

2. If the process is going to be old and requires some type of change, then maintenance or some enhancements can be done in the project.

3. It is the realistic approach to be used.

4. The main and most important feature of this model is risk analysis. The risk analyst will try to reduce the risks raised. Prototyping can be used as risk reduction mechanism.


1. Customer Satisfaction: It is very hard to satisfy the customer that the evolutionary approach will be controlled.

2. Risk Analysis:  This approach requires a risk analyst or experts to handle the risks properly. If risks are not covered initially then may arise at any time in later stages.

3. Slow Speed:  This model cannot be sued frequently so results are not available soon.

4. High Cost:  It requires a large sum of money to be completed.

5. Very Difficult to Implement; Spiral model requires much effort to be implemented.

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