What is Spiral Model? When to Use? Advantages & Disadvantages

The Spiral Model is primarily leveraged to manage large-scale and challenging software development processes, allowing for a more flexible and adaptable approach to development. Implementation of spiral model is best suited on projects with high-risk level. 

Risk management is crucial for any software development project. Besides, the development team seeks a cost-effective and easy approach to streamline the software development process. With the “Spiral Model of Software Development and Enhancement” being coined under the guidance of Barry Boehm in 1986, it has turned out to be one of the most streamlined iterative development processes. 

Let’s learn more about the spiral model to understand its workings and the reasons behind its success.

Understanding Spiral Model

The spiral model is an SDLC standard that merges components of a waterfall model and an iterative software development model. It enables the product to be released and updated in every phase of the spiral. It is worthwhile to use this model for large and complex projects. 

It can develop prototypes at every stage. A prototype is developed at every phase’s beginning and works as a risk management technique. It is a developing risk-driven approach that works as the latest system for managing the software process.

Specific activities are performed in every spiral. Each spiral’s output is a tiny prototype of the large software. Similar activities are then iterated for all the spirals until the whole software is developed. Usually, the spiral radius denotes the estimated project development cost.

Moreover, the angular dimension denotes the development that has happened till now. Depending on additional requirements, additional functionality will be incorporated into the product in each increasing spiral. This continues until the product is prepared for the production phase.

Spiral Model Phases

The spiral model of software development is categorised into various phases. Each of these phases contributes as a small part of the software development. Each phase is tested at the end of each part. Note that these phases don’t have a fixed count; they vary based on the project. Each phase begins with design objectives and concludes with a client review.

This model develops a software product in incremental series. There are various tasks in which each phase activates.

Here are the 5 phases of the spiral model

1) Define objectives and discover alternate solutions

2) Risk analysis and resolving

3) Develop and test

4) Evaluation

5) Review and plan the next phase

Each phase of the model is categorised into four quadrants. Let’s dive deeper to understand the functions of these four quadrants in-depth-

1) Define objectives and discover alternate solutions

The first phase determines the project’s scope and creates a plan for the subsequent iteration of the spiral. It involves tasks like gathering requirements and analysis. Depending on these requirements, objectives are stated, and various alternate solutions are recommended.

Generally, the spiral model gathers two types of requirements, i.e. BRS (Business requirement specification) and SRS (System requirement specifications).

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2) Risk analysis and resolution

This phase analyses all the recommended solutions. Moreover, any potential risk is recognised, analysed, and resolved. An alternative solution is discussed and executed based on the risks that arise.

It also involves prototype creation. In addition to identifying potential risks, it also arranges and finalises the risk mitigation strategy.

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3) Develop and test

This phase is the core of the spiral model process. This is because it implements various essential features. All the executed features are verified with exhaustive testing. Once the product development completes, the phase tests, codes, and deploys software on the client side.

4) Evaluation

This phase evaluates the software to learn if it fulfils the customer’s requirements and whether it is of high quality or not. It also involves recognising risks.

5) Review and plan the next phase

The customer evaluates the developed software in this phase. Based on the evaluation outcomes, the subsequent iteration of the spiral starts with a new planning phase.

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When to use the Spiral Model?

You shall use the spiral model of software development when:

  • The developed project is large.
  • The software development project involves the development of a prototype.
  • The software development project prioritises risk and cost assessment.
  • The software development projects involve medium to high-risk.
  • The defined requirements are complex.
  • The customers expect the releases to stay continuous.
  • You require the release of your software development in phases instead of as a whole.
  • You expect time-saving and work flexibility.
  • You expect changing requirements.
  • If you can’t invest in a long-term project owing to your company’s financial situation or the economic climate.

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Spiral Model Advantages

  • The spiral model is ideal for large, complex projects because continuous prototyping and evaluation help mitigate any risk.
  • Its risk-handling capability makes it ideal for critical projects. The spiral model example can be software related to the health sector, game development, space exploration, etc.
  • It allows client feedback and execution of change requests (CRs). Based on the client feedback, constructive changes can be brought into the software.
  • There are high odds of customer satisfaction because customers can view a prototype in every phase.
  • The cost estimation is simplified because the prototype building happens in tiny chunks.
  • It prioritises continuous or recurring development that simplifies risk management.
  • It enables quick development, incorporating the highlights into a systematic path.
  • It facilities regular assessments and reviews that enrich communication among the development team and their customers.
  • The multiple iterations of the software development process lead to enhanced software quality and reliability.
  • All the specific requirements required at later stages can be accurately included.

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 Spiral Model Disadvantages

  • The spiral model is not suited for smaller and simpler projects since it involves multiple phases.
  • Implementing it can be complex since it involves multiple iterations of the software development process.
  • The spiral model diagram illustrates the inclusion of several intermediate stages. So, it needs more documentation compared to other software development models.
  • It is time-consuming and expensive due to the risk analysis, prototype development, and multiple evaluations and reviews in each phase.
  • The project’s completion significantly depends on risk analysis. The project development through this project can be unsuccessful in the absence of extremely experienced experts.
  • Project deadlines can’t be fulfilled due to an unknown number of phases in the beginning, risk analysis, and frequent prototyping.
  • It poses a risk of exceeding the budget.
  • It demands considerable investment in planning, risk assessment, and evaluation.
  • It is difficult to estimate the time of the project’s completion because the number of phases is unknown at the project’s beginning.
  • It demands exceptional risk evaluation expertise.

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The spiral model benefits large, cost-effective, complex, and risk-driven software development projects. Since it allows users to update during the development procedure, it significantly saves additional maintenance costs. Its efficient risk analysis and resolving ability streamline software development with improved customer satisfaction and optimum utilisation of resources towards maximum value. 

Q. How can you ensure customer satisfaction using the spiral model?

The spiral model simplifies customer feedback. If you’ve designed software for a customer, the customer would be able to see and analyse their product in each phase. Consequently, you can learn their opinions and make necessary changes before the product is completely developed. Hence, the spiral model saves time in development and reduces expenses.

Q. What are the common examples of the spiral model?

The best spiral model example is that Microsoft used it to create early versions of Windows. This model was also used to develop Gantt chart software. Moreover, the game development industry uses it to develop cutting-edge games.

Q. Why is the spiral model considered costly?

Implementing the spiral model needs experienced resources because risk analysis is a vital phase of this model. The risk analysis needs high-level expertise; therefore, this model is costly.

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