Key Difference – Waterfall vs Spiral Model
The key difference between waterfall and iterative model is that waterfall model is used for smaller projects and projects with clear requirements while the spiral model is used for large, complex projects that require continuous risk analyzing.
Software Development Life Cycle (SDLC) is a process followed by a software organization to develop a software project. There are various software development life cycle models which can be followed during the software development process. These models are known as software development process models. Waterfall and Spiral Model are two of them.
CONTENTS
1. Overview and Key Difference
2. What is Waterfall Model
3. What is Spiral Model
4. Side by Side Comparison – Waterfall vs Spiral Model in Tabular Form
5. Summary
What is Waterfall Model?
Waterfall model is a software development process model with a linear sequential flow. One phase starts after the completion of the previous phase. There is no overlapping between the phases. In this approach, the whole software development process is divided into phases. The outcome of one phase becomes the input for the next phase.
The first phase is to the requirement gathering and analysis. In this phase, the requirements necessary for the project is collected and analyzed. Then they are documented. This document is called the Software Requirement Specification (SRS). Next phase is design phase. The system design helps to define the overall system architecture. In the implementation phase, the system is developed in small units. Each unit is tested and all the units are integrated into a complete system and tested in the integration and testing phase. After the testing is completed, the product is released to the market. It is the deployment phase. Finally, new enhancements and further improvements are added to the product in the maintenance phase.
Figure 01: Waterfall Model
Waterfall model is simple and easy to understand. It is easy to arrange tasks and to understand milestones. Only one phase is processed and completed at a time. Waterfall model is not suitable to develop complex projects. Also, it is not suitable for a project with changing requirements.
What is Spiral Model?
The spiral model was introduced as an alternative to waterfall and prototype model. The main focus of the spiral model is to analyze risk. The phases of the spiral model include planning, risk analysis, engineering, and evaluation. The software project continuously passes through these phases in iterations called spirals.
Figure 02: Spiral Model
The base spiral starts with planning. Identifying the system and subsystem requirements are done in this phase. The Software Requirement Specification (SRS) is developed using the gathered requirements. Risk analyzing phase is to identify the risks associated with the project. If there are any risks, alternative solutions are suggested. A prototype is produced at the end of this phase. In the Engineering phase, software development and testing occur. In the evaluation phase, the output is shown to the customer to get a feedback. If the customer approved, the project can continue to the next spiral. Again the project goes through the above phases.
Spiral model is more suitable for large and complex projects. It is suitable for a project that requires continuous risk analysis. It provides more control towards all phases of development. The risk analyzing might require expert employees and the spirals might take a long time. Also, it is not a suitable model for small projects. Those are some drawbacks of the spiral model.
What is the Difference Between Waterfall and Spiral Model?
Waterfall vs Spiral Model |
|
| The waterfall model is a relatively linear sequential design approach to develop software projects. | The spiral model is a risk driven process model generator for software projects. |
| Customer Involvement | |
| In waterfall model, the customer involvement is minimum. | In spiral model, the customer involvement is high. The customer has an awareness of what the product is. |
| Flow of the Phases | |
| In waterfall model, after completing a phase and reached a new phase, it is not possible to go back to the previous phase. | Spiral model operates on iterations so it is possible to go back to the previous phases. |
| Usage | |
| The waterfall model can be used for small projects and for projects with clear requirements. | The spiral model can be used for large, complex project that requires continuous risk analyzing. |
| Simplicity | |
| The waterfall model is simple and easy. | The spiral model is a complex model. |
Summary – Waterfall vs Spiral Model
Two software process models are waterfall and spiral model. The difference between waterfall and spiral model is that waterfall model is used for smaller projects and projects with clear requirements while the spiral model is used for large, complex projects that require continuous risk analyzing.
Reference:
1.“SDLC Waterfall Model.”, Tutorials Point, 8 Jan. 2018. Available here
2.“SDLC Spiral Model.”, Tutorials Point, 8 Jan. 2018. Available here
Image Courtesy:
1.’Spiral model (Boehm, 1988)’ By Connyderivative work (Public Domain) via Commons Wikimedia
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