Spiral Model in Software Engineering: What is it?

The spiral model is one of the most important models in SDLC, possessing similar qualities as that of the incremental model which mainly focuses on risk analysis. Furthermore, it offers an incremental release of products, the released product is refined via each spiral phase, and it provides the opportunity for the developer to create prototypes at each level. The main purpose of the creation of this model is to manage unknown risks once the project has started.

Points to be covered:

• What is Spiral Model?
• Why Spiral Model?
• Phases of Spiral Model
  • Steps involved in Spiral Model
• Difference between Spiral Model and Waterfall Model
• Advantages of Spiral Model
• Disadvantages of Spiral Model
• Application of Spiral Model
  • Possible use cases of Spiral Model
• Conclusion

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What is Spiral Model?

In SDLC, Spiral Model refers to the type of software development model where risk analysis handling is supported, and new changes are made accordingly in each newly released phase that is risk-free.

• It was initially presented in a paper written by Barry Boehm, an American software developer in 1986.
• The spiral approach binds the advantages of the waterfall and iterative methods, combining their strengths while also addressing any functional gaps present.
• The flaws in the program written are described in depth, and alternate fixes are recommended if necessary.
• For the software development process, spiral uses the approach of the Prototyping Model where the different phases of the software are released until the desired results are achieved.

• The spiral model consists of multiple loops which represent the phases of the development process, whereas the radius represents the cost of the project according to the phase being processed.
• Because it incorporates all the other SDLC models, and is also known as a Meta-Model.
• Risk management is carried out under the Spiral Model, where risk is defined as a potential bad circumstance that may have an impact on the project’s success.

Now we know what is meant by the spiral model, let’s move forward and have a look at why we need it.

Why Spiral Model?

Check out the below-distinguishing pointers because of which one should opt for Spiral Model while developing software.

• Spiral Model fills in the gaps during the development process by including elements from all SDLC models, which makes it more reliable than other SDLC models.
• Feedback is present in it at the end of every phase, user feedback is taken which is rectified then another phase is worked upon.
• Risk management was first introduced in the spiral model, making it the best model for software development.
• The addition of new functionality is possible in the later stages.
• The spiral model makes the scope for improvement in the software product to be delivered.

Let’s continue with the flow of getting familiar with the spiral model. Now check out the different phases of it.

Phases of Spiral Model

Steps involved in Spiral Model

The stages involved in putting the Spiral model into practice are listed below:

• In step one, the new system requirements are defined in detail as much as possible.
  • Insights are taken from internal and external sources namely from users based on their experience with the previously available system.
• Based on the insights from the previous step a new prototype is prepared. 
• The initial prototype of the new system is built using the proposed project. This system, which resembles the properties of the final products, is often a smaller one.
• A second prototype is developed using the following four steps:
  • Assessing the initial prototype for its advantages, disadvantages, and associated potential risks.
  • Defining the second prototype’s specifications.
  • Creation of a second prototype and planning its design.
  • Building and testing a second prototype.
• The entire project may even be abandoned if the risk is determined to be of severe rating.
  • Risk factors might include underestimating operating costs, overspending on development, and other issues that could result in a poor final product.
• The current prototype is assessed in the same way as the previous prototype, and if more testing is required, another prototype is created from it using the four-step process described above.
• The previous processes are repeated until the client is certain that the improved prototype accurately depicts the intended final product.
• Based on the improved prototype, the finished system is built.
• The finished system undergoes extensive testing and evaluation. Continuous routine maintenance is performed to avoid catastrophic breakdowns and reduce downtime.

Below mentioned are the four different phases of the spiral model, which also depict the actual working of it.

• Objective determination and recommendations:
  • In this phase of the spiral model, detailed information is gathered from various internal and external sources.
  • Users/clients are also involved in this process, their role is to provide the software specifications which act as the inputs in the software development process.
  • After analyzing the gathered information alternative solution is prepared and worked upon. It is represented in the first quadrant of the above-mentioned diagram.
• Identification and Rectification of Risks:
  • This phase is represented by the second quadrant of the above-mentioned diagram.
  • In this phase, all the possible solutions to the potential problem are considered and after the evaluation, the most optimized one is selected.
  • At the end of this phase, a prototype is prepared based on the most optimized solution selected.
• Development of the next version:
  • This phase of the spiral model is represented in the third quadrant.
  • In this phase, various type of testing is carried out after the evaluation of results from the previous version.
  • By the end of this phase new features are identified and developed.
• Review and Planning:
  • This is the final phase of the spiral model represented in the fourth quadrant.
  • In this phase where user/client interacts and evaluates the developed version of the proposed software.
  • At the end of this, planning for the next version has started.

Difference between Spiral Model and Waterfall Model

Both of these models have some features and uppercuts on each other, let’s have a look at them. Read the below-mentioned pointers to get the detailed difference between these two types of SDLC models.

Advantages of Spiral Model

In this section, below-mentioned points are the advantageous pointers because, of which Spiral Model exists in the market:

• In the spiral model, further modifications can be made in the later stages of the development cycle.
• Cost estimating is quite simple since the project is divided into manageable sections.
• Recurrent development aids in risk detection and rectification.
• In the spiral model, there is a rapid development of software components which makes development faster.
• User input is possible in the spiral model, which helps the developers to get insights into the released prototype.
• The spiral model is preferred for large projects because it becomes easy for breaking the whole software project into smaller project components, which makes it easy to apply the principles of the spiral model.

Disadvantages of Spiral Model

The factors which the spiral model lacks, making it not the first choice of the developers:

• Risk management is the only key principle of the Spiral model, which shows its dependency on risk management.
• It possesses high complexity while on implementation as compared to other SDLC models.
• The time taken for project completion remains unknown till the product is delivered as it is developed in small components and changes are incorporated in between the project development life cycle.
• The Spiral model needs to be properly documented, as multiple phases are released.
• Although there is less client engagement, the spiral approach primarily addresses numerous unexpected risks.
• It works well for projects that are vulnerable to a variety of risks that are difficult to identify in the early stages of the project.
• The spiral model cannot work for smaller projects.

Application of Spiral Model

Possible use cases of Spiral Model

Consider the below-mentioned points which state possible use cases of the spiral model:

• Software requiring regular releases.
• Initiatives that are long-term yet are not possible because of changed economic considerations.
• Software projects with medium to high potential risk.
• Projects that consider cost and risk assessments.
• A prototype might be advantageous for some tasks undertakings with ambiguous or complicated requirements.

Interested to learn more about prototype models, check out our Prototype model in Software Engineering blog.

Conclusion

Risk management is one of the most important parts of software development, and the spiral model offers it. In the blog, we have talked about the pros and cons of it, their applications, and the whole working process. There are many multiple alternatives available to the spiral model but it is still one of the most trusted SDLC models, MNCs like Microsoft still use it. If anyone aspiring to be a software engineer then having a good grasp of the spiral model can help them to develop better fault-tolerant software.

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