The spiral model was proposed by Bohem.
In spiral model the radial dimension represents the cumulative cost incurred in finishing the steps so far and angular dimension represents the progress made in completing each cycle of the spiral.
In the first quadrant of the spiral model each cycle begins with the identification of objectives for that cycle, the alternatives possible for achieving objectives and the constraints.
The next step is to evaluate these different alternatives based on objectives and constraints. The evaluation in this step is based on the risk perception of the project.
The next step is to develop strategies that resolve the risks, this step involves activities like bench marking, simulation etc.
After this the software is developed keeping in mind the risks and finally next stages are planned.
What Are the Phases of the Spiral Model?
The Spiral Model is risk-driven, focusing on managing risk through multiple iterations of the software development process. It consists of the following phases:
Planning:
The first phase of the Spiral Model is the planning phase, where the project’s scope is determined, and a plan is created for the next spiral iteration.
Risk Analysis:
In the risk analysis phase, the risks associated with the project are identified and evaluated.
Engineering: In the engineering phase, the software is developed based on the requirements gathered in the previous iteration.
Evaluation:
In the evaluation phase, the software is evaluated to determine if it meets the customer’s requirements and is of high quality.
Planning:
The next spiral iteration begins with a new planning phase based on the evaluation results.
The Spiral Model is often used for complex and large software development projects, allowing for a more flexible and adaptable approach to software development. It is also well-suited to projects with significant uncertainty or high levels of risk.
Each phase of the Spiral Model is divided into four quadrants. The functions of these four quadrants are discussed below-
Objectives determination and identify alternative solutions:
Requirements are gathered from the customers, and the objectives are identified, elaborated, and analyzed at the start of every phase. Then, alternative solutions possible for the phase are proposed in this quadrant.
Identify and resolve Risks:
During the second quadrant, all the possible solutions are evaluated to select the best solution. Then, the risks associated with that solution are identified and resolved using the best possible strategy. At the end of this quadrant, the Prototype is built for the best possible solution.
Develop the next version of the Product:
During the third quadrant, the identified features are developed and verified through testing. At the end of the third quadrant, the next version of the software is available.
Review and plan for the next Phase:
In the fourth quadrant, the Customers evaluate the so-far developed version of the software. In the end, preparing for the next phase is started.
Risk Handling in Spiral Model
A risk is any adverse situation that might affect the successful completion of a software project. The most important feature of the spiral model is handling these unknown risks after the project has started. Such risk resolutions are more accessible by developing a prototype. The spiral model supports coping with risks by providing the scope to build a prototype at every phase of software development.
The Prototyping model also supports risk handling, but the risks must be identified entirely before the start of the development work of the project. But in real life, project risk may occur after the development work starts; in that case, we cannot use the Prototyping Model. In each phase of the Meta Model, the product features are dated and analyzed, and the risks at that point in time are identified and resolved through prototyping. Thus, this model is much more flexible compared to other SDLC models.
Why Spiral Model is called the Meta Model?
The Spiral model is called a Meta-Model because it subsumes all the other SDLC models. For example, a single loop spiral actually represents the Iterative Waterfall model. The spiral model incorporates the stepwise approach of the Waterfall model. The spiral model uses the approach of the Prototyping model by building a prototype at the start of each phase as a risk-handling technique. Also, the spiral model can be considered as supporting the Evolutionary model– the iterations along the spiral can be considered as evolutionary levels through which the complete system is built.
Advantages of the Spiral Model
Below are some advantages of the Spiral Model.
Risk Handling: The projects with many unknown risks that occur as the development proceeds; in that case, the Spiral Model is the best development model to follow due to the risk analysis and risk handling at every phase.
Suitable for large projects: Using the Meta Model in large and complex projects is recommended.
Flexibility in Requirements: Change requests in the Requirements at a later phase can be incorporated accurately by using this model.
Customer Satisfaction: Customers can see the development of the product at the early phase of the software development and thus, they habituated with the system by using it before completion of the total product.
Iterative and Incremental Approach: The Meta Model provides an iterative and incremental approach to software development, allowing flexibility and adaptability in response to changing requirements or unexpected events.
Emphasis on Risk Management: The Meta Model strongly emphasizes risk management, which helps minimize the impact of uncertainty and risk on the software development process.
Improved Communication: The Meta Model provides regular evaluations and reviews, enhancing customer and development team communication.
Improved Quality: The Meta Model allows for multiple iterations of the software development process, which can result in improved software quality and reliability.
Disadvantages of the Spiral Model
Below are some of the main disadvantages of the spiral model.
Complex: The Meta Model is much more complicated than other SDLC models.
Expensive: The Meta Model is not suitable for small projects as it is costly.
Less dependability on Risk Analysis: The successful completion of the project is very much dependent on Risk Analysis. Without very highly experienced experts, it will be a failure to develop a project using this model.
Difficulty in time management: As the number of phases is unknown at the start of the project, time estimation is complicated.
Complexity: The Meta Model can be complex, as it involves multiple iterations of the software development process.
Time-Consuming: The Meta Model can be time-consuming, requiring multiple evaluations and reviews.
Resource Intensive: The Meta Model can be resource-intensive, requiring a significant investment in planning, risk analysis, and evaluations.
The most serious issue in the cascade model is that it takes a long time to finish the item, and the product becomes obsolete. To tackle this issue, we have another methodology known as the Winding or spiral model. The winding model is otherwise called the cyclic model.
