This post talks about a development methodology termed as the “Spiral Model” development approach. We discuss its features, advantages and disadvantages, and explore its uses in software engineering.
What is Spiral Model? An Introduction to the Spiral Model
A basic definition and outline of what the spiral model is that it can be classified as a risk-driven software development process model. Depending on the unique risks patterns associated with a project, the spiral model serves as a guide to adopt one or more elements of various process models.
The spiral model stems from a paper by Barry Boehm in 1986, “A Spiral Model of Software Development and Enhancement”. Boehm speaks about how the risks of a project and its possible choices can pose an appropriate process model through the use of Spiral Model approach.
The spiral model consists of four phases: Planning, Risk Analysis, Engineering, and Evaluation. A typical project goes through each of these phases in iterations, which in this case can be termed as spirals. It all starts from the baseline spiral, which begins from the Planning phase, where requirements are gathered and assessed. All subsequent spirals build upon the baseline spiral.
The Four Phases of Spiral Model:
1. Planning
In this phase project requirements, details, and scope is established in the form of Business Requirement Specifications ‘BRS’ and System Requirement Specifications ‘SRS’. The development team builds an understanding of product and project and conceptualizes on design options, whilst considering factors such as costs, technology, usage, and timelines.
2. Risk Analysis
Identification of potential risks that may arise, and consequently, mitigation strategies planned and built to counter those risks.
3. Engineering
The software is developed, tested and deployed using a waterfall or incremental development approach. The sequential cycles and assessments of the product at each stage go through an evolving process forming the end product or project.
4. Evaluation
All current developments and output is assessed and evaluated against intended requirements and objectives before it moves on to the next spiral. Faults and lapses, if any, are identified and corrective measures taken to rectify.
The Advantages and Disadvantages of Spiral Model
Below we list some of the key advantages and disadvantages of using a software development approach such as the spiral model:
| Advantages of Spiral Model | Disadvantages of Spiral Model |
|---|---|
| Due to a great degree of risk analysis, any potential risks are pre-anticipated and averted. | Suitable only for large projects and demands a certain degree of risk assessment expertise |
| Enables greater flexibility | Increased documentation due to the number intermediate phases |
| Efficient and effective development | Costly as compared to other software development approaches as spiral may continue indefinitely |
| Best suited for large, complex and mission-critical projects | Spiral development is viewed as a complex process |
| Clients have greater visibility and can review at different stages of development | Milestones and project deadlines are difficult to define and ascertain |
| A well-documented focus and control enabled | |
| Leaves space for additional post-project functionalities | |
| A more realistic and objective cost estimation as prototype building is done in fragments |
When to Use the Spiral Model Approach to Development
Recommending the use of spiral model approach for development and projects should be based on the following factors:
- Where there is a budget constraint and risk evaluation is critical
- Large projects of higher project value and investment
- Where there are concurrent changes and new requirements and alterations develops as it progresses
- Projects that require a prototype to test viability and feasibility
- Projects that require frequent releases or launch in phases
- When advantages of spiral model outweigh its disadvantages
Want to know more about the spiral model and its implementation for your project? Contact us to assess its suitability or an assessment for the best development approach for you.