The spiral model is one of the most important models in SDLC, possessing similar qualities to 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.
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What is Spiral Model?
In SDLC, the Spiral Model refers to a type of software development model where risk analysis and handling is supported, and new changes are made accordingly in each newly released phase that is risk-free.
Few Facts About Spiral Model:
- 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 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 distinguishing points below to see why you should use the spiral model when 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 at the end of every phase; user feedback is taken, which is rectified, and 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 provides 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
The four different phases of the spiral model are described below, as well as how it works in practice.
- 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, an 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.
- During this phase, the user/client interacts with and evaluates the developed version of the proposed software.
- At the end of this, planning for the next version has started.
How the Spiral Model Works (Step-by-Step Process)
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.
- Developing and designing a second prototype.
- Building and testing a second prototype.
- The entire project may even be abandoned if the risk is determined to be of a 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 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.
Spiral Model vs. 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.
| S.No | Waterfall Model | Spiral Model |
| 1. | The implementation process of the waterfall model is simple and easy. | Implementation of the spiral model is complex and requires a lot of resources. |
| 2. | The working principle of the waterfall model is sequential. | The working principle of the spiral model is evolutionary. |
| 3. | Error identification and rectification are performed after each stage. | Error identification and rectification are done in between the processes. |
| 4. | It is preferred for smaller projects. | It is preferred for larger projects. |
| 5. | Risk analysis and management are absent in the waterfall model. | Risk analysis and management are present in the spiral model. |
| 6. | Customer involvement is minimal. | Customer involvement is maximal. |
Why Spiral Model is the Blueprint for Risk-Free Software Development
Software development is always brimming with risks. Cost overruns, missed deadlines, security loopholes, and subsequent changes in requirements are common grievances on software projects. The Spiral Model solves these issues by injecting risk analysis at every phase of development, thereby making it the gold standard in software development with little to no risk.
What Makes the Spiral Model Risk-Free?
| Risk Factor | Traditional Development Models | Spiral Model Approach | Why It’s Better? |
| Changing Requirements | Tough to adjust when the development starts. | Iterative Development permits constant improvement. | Prevents expensive redesigns. |
| Budget Overruns | Fixed budget, unforeseen expenses. | Risk assessment helps in cost estimation. | Financial foresight. |
| Security Issues | Security added too late in the development process. | Security risks are examined with each iteration. | Improves accuracy in security issues. |
| Project Failure Risks | No warning signs in the early stages. | Risk assessment stage identifies feasibility issues. | Saves time & resources. |
How the Spiral Model Eliminates Common Software Development Risks
- Requirements are Obscure or Evolving
Observation: A majority of software development projects fail due to unclear or shifting requirements.
Solution: Spiral Model
- In each phase, requirements are evaluated and revised.
- Customers and stakeholders provide feedback regularly.
- New requirements are incorporated in the subsequent cycle to avoid scope creep.
Example: A healthcare management system must comply with government regulations while also ensuring that existing features are not disrupted, resulting in multiple iterations.
- Financial Risks and Budgetary Overruns
Observation: Development costs in a fixed-cost model are often underestimated, leading to budget losses.
Solution: Spiral Model
- Each cycle of the model examines costs, thereby reducing unaccounted-for financial risks.
- Allows for changes in feature and scope based on budget availability.
- Only validated features are developed, minimizing effort waste.
Example: A banking software project using the waterfall model cost $7 million instead of the expected $5 million. The spiral model used feasibility tests to avert cost overruns.
- Security & Cyber Threats
Problem: Security measures are typically an afterthought and incorporated towards the end of the development process, which leaves systems open to external threats.
Solution: Spiral Model
- Security measures are considered at every stage. They are not treated as an afterthought.
- Each iteration of the project includes penetration testing and security audits.
- Irrespective of the timeframe security industry compliance, such as GDPR, HIPAA, and ISO 27001, is included.
Example: A cloud provider implementing encryption protocols at the start of platform development ensures data privacy before scaling the platform.
- High Failure Rate in Large-Scale Projects
Problem: Poor control of risks is a fundamental reason most large-scale projects remain unsuccessful.
Solution: Spiral Model
- Risks are evaluated and prioritized for each phase.
- If risks are too high, solutions or project cancellation can occur before money is spent, and the results are irreversible.
- Stakeholders receive early working prototypes for validation of concepts.
For example, NASA uses the spiral model for mission-critical space software development to prevent failure during extreme deployments.
Advantages of Spiral Model
In this section, the following 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 to break 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 that the spiral model lacks make 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 is highly complex while being implemented 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.
Applications and Real-World Use Cases
The Spiral Model is applied in software projects that are very high-risk, of large scale, and security-oriented. It is widely accepted to incorporate risk analysis, iterative enhancement, and customer feedback in development processes for industries that highly value integration and modification.
In this section, we will analyze the practical applications of the Spiral Model, alongside its case studies from different companies and sectors.
| Industry | Why is the Spiral Model Used? | Example Projects |
| Aerospace & Defense | High-risk applications need fail-safe software. | NASA’s Mars Rover & space mission software |
| Banking & Finance | Security and compliance risks need to be addressed early. | Fraud detection systems, online banking platforms |
| Healthcare & Medical Software | Software needs to be HIPAA, GDPR, and FDA compliant. | Medical imaging software, management of patient records |
| E-Commerce & Retail | Scalability and security risks need to be mitigated iteratively. | Amazon’s recommendation engine, payment gateways |
| Cybersecurity & Data Protection | Continuous updates are necessary to combat new threats. | Intrusion detection systems, encryption software |
| Gaming & Virtual Reality | Performance optimization and risk analysis are essential. | AAA gaming engines, VR-based applications |
The Spiral Model provides stability, security, and ongoing improvements, and it is perfect for projects where failure cannot be an option.
Conclusion
The Spiral Model represents more than just a software development lifecycle (SDLC) model. It is a strategy with a defined set of parameters for ensuring cost-effective, secure, and scalable software development within an organization.
Traditional models like Waterfall and Agile have included customer feedback but not risk assessment. When it comes to managing large and high-risk projects, the Spiral Model outperforms Waterfall and Agile methodologies due to its combination of iterative development, continuous risk assessment, and feedback.
Want to learn more about software development models? Read our blog on SDLC methodologies for a comparison of Agile, Waterfall, and Iterative Model.