Spiral Model in Software Engineering

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The spiral model is a risk-based software development approach. It guides a team to adopt components of one or more process models, such as incremental, waterfall, or evolutionary prototyping, based on the particular risk patterns of a given project.

The spiral model is one of the best software development life cycle models due to the following properties:

  • Risk management is present in the model.
  • The Spiral model is also popular due to its ability to adapt to changes.
  • Frequent feedback from the client.

What is Spiral Model in Software Engineering?

It is an evolutionary process model that combines prototyping's iterative nature with the linear sequential model's regulated and systematic characteristics. It implements the capability of rapid production of new software versions. The program is developed in a series of incremental releases using the spiral methodology.

The spiral model is one of the most prominent Software Development Life Cycle models for risk management. It resembles a spiral with several loops in diagrammatic depiction. The spiral's exact number of loops is unclear, and it varies from project to project.

In the software development process, a "phase" is defined as each loop of the spiral.

Depending on the project risks, the project manager might change the number of phases required to build the product. In developing a product utilizing the spiral model, since the number of phases is dynamically determined by the project manager, therefore, the project manager plays a very important part.

In the SDLC Spiral model, the development process begins with a limited set of needs and progresses through each development phase for that set of criteria. Until the application is ready for production, the software engineering team adds functionality for the increased requirement in every increasing spiral. The spiral's radius at any point symbolizes the project's expenses (cost) thus far, while the angular dimension represents the current phase's progress. what is the spiral model

Spiral Model Phases

Each phase or cycle in the spiral is divided into four quadrants, and this phase or cycle is followed in an iterative manner till the project gets completed.

Four quadrants of the spiral model are:

  1. Objectives determination and identify alternative solutions.
  2. Risk Assessment and reduction.
  3. Develop and Validate the project.
  4. Planning and Review**.

1) Objectives Determination and Identify Alternative Solutions

The baseline spiral is used to collect the business needs at this phase.

This phase is followed by the identification of system requirements, subsystem requirements, and unit requirements as the product mature. At the outset of each step, customers' requirements are gathered, and objectives are identified, elaborated, and analyzed. Then, in this quadrant, alternative solutions for the phase are given.

It includes estimating the iteration's cost, timeline, and resources. A thorough understanding of the system's needs in order for the system analyst and the customer to maintain constant communication is also involved in this quadrant.

2) Risk Assessment and Reduction.

In the second quadrant, all viable solutions are reviewed in order to choose the optimal one.

The risks connected with that solution are then identified, and the risks are minimized using the best technique possible. The Prototype is made at the end of this quadrant for the finest potential solution.

Technical feasibility and management risks, such as schedule slippage and cost overrun, are identified, estimated, and monitored through risk analysis. While a risk mitigation strategy is being created and finalized, possible risks are being identified.

3) Develop and Validate the Project

This quadrant has ways to deal with the risks, and uncertainties; benchmarking, simulation, and prototyping are all possible components of this process.

At every spiral, this phase corresponds to the real software product's production. In the baseline spiral, a POC (Proof of Concept) is created to collect user feedback when the concept is merely being thought of and the design is being developed.

Then, as needs and design specifics become clearer in succeeding spirals, a functioning model of the program known as a build with a version number is created. The features found in the third quadrant are developed and tested.

The software's next version becomes available at the end of the third quadrant.

4) Planning and Review

Finally, the next step is planning and reviewing. The project is evaluated, and the decision is made whether to continue with the spiral for another time. If it is decided to keep it, plans for the next stage of the project are written up. The development phase is determined by the risks that remain. If performance or user-interface risks are deemed more important than program development risks, the next phase could be an evolutionary development that includes the creation of a more thorough prototype to address the issues. Each stage of the spiral is finished by a review that covers all of the products generated during that cycle, as well as preparations for the following cycle, which is an important aspect of the concept. The spiral model can be used for both development and upgrade projects.

Customers evaluate the software that has been built thus far in the fourth quadrant. Identifying and monitoring risks such as schedule slippage and cost overrun are also part of the job.

When to Use Spiral Model?

The Spiral Model is commonly employed in the software industry because it is in line with any product's natural development process, i.e., learning with maturity while posing the least amount of risk to both the customer and the development business.

The following pointers describe how a Spiral Model is commonly used :

  1. For projects with a medium to a high level of risk.
  2. When there is a budget restriction, risk assessment is critical.
  3. The customer is unsure of their requirements, which is common.
  4. Long-term project commitment due to the possibility of shifting economic priorities as requirements change over time.**

Spiral Model Applications

  1. Spiral approach is utilized when frequent releases are necessary.
  2. When committing to a long-term project is no longer feasible owing to shifting economic priorities.
  3. When working on a huge project, a spiral model is utilized in software engineering.
  4. Requirements are difficult to understand and must be evaluated.

Risk Handling in the Spiral Model

The Prototyping Model also enables risk management, although hazards must be fully identified before the project's development activity begins. However, in real life, project risk may arise after development work has already started; in this scenario, the Prototyping Model cannot be used.

The product's features are evaluated and examined in each phase of the Spiral Model, and the risks at that moment in time are identified and resolved through prototyping.

As a result, this paradigm is far more adaptable than other SDLC models. Any adversity that could compromise the effective execution of a software project is referred to as a risk. The spiral model's most essential aspect is how it handles unforeseen hazards once the project has begun.

The development of a prototype makes such risk resolutions easier. The spiral approach encourages risky copying by allowing for the creation of a prototype at each stage of software development.

Advantages of Spiral Model

  1. Due to the risk analysis and risk management at each phase, the Spiral Model is the best development model to follow for projects with many unknown hazards that arise as the development progresses.
  2. The Spiral Model is suitable for large and complex projects as development can be broken down into smaller chunks, with the risky elements being done first, allowing for better risk management.
  3. Because the prototype is built in small pieces, cost estimating is simple.
  4. Spiral growth is quick, and features are added in a systematic manner.
  5. Using this paradigm, change requests in the Requirements at a later stage can be accurately implemented.
  6. Customers can observe the product's progress throughout the early stages of software development and so become familiar with the system by using it before the final product is completed.

Disadvantages of Spiral Model

  1. Risk Analysis plays a critical role in the project's success. The development of a project employing this strategy will be a failure without a large number of highly experienced professionals.
  2. The spiral model is not appropriate for small projects due to its high cost.
  3. Time estimation is challenging because the number of phases is unknown at the outset of the project.
  4. Spiral model protocol must be properly followed for smooth operation.
  5. Management is more difficult. It's possible that the project's end date will not be known until later.
  6. Spiral could continue endlessly as due to a large number of phases, there is always a scope of increasing or changing the requirements.
  7. A large number of intermediate phases necessitates a lot of paperwork.


  1. The Spiral Model is one of the best Software development life cycle models due to its efficiency in dealing with complex projects and the risk analysis which is made in the project.
  2. The most important factors which other SDLC models lack, such as Risk Analysis, Frequent customer feedback, Changing requirements, Quick Delivery, etc.
  3. Risk handling in the Spiral Model helps us in analyzing the risks which can be countered during the life cycle of the software development.
  4. Some of the major factors which make the spiral model not suitable for use are such as Time estimation is challenging, high cost, difficult management, and highly experienced professionals are needed.
  5. Risk Handling is a very important part of the software development life cycle. Risk handling helps in analyzing and minimizing the obstacles which occur while developing the software.