The cascade model ( English waterfall model , sometimes translated as the "Waterfall" model ) is a model of a software development process in which the development process looks like a stream that goes through phases of requirements analysis, design, implementation, testing, integration and support. The source is often referred to as an article published by W. W. Royce in 1970 ; while Royce himself used an iterative development model .
| Software development | |
|---|---|
| Software development process | |
| Key processes | |
| Analysis • Design • Programming • Documentation • Testing | |
| Models | |
| Iterative • Spiral • Cascading • V-Model • Dual Vee Model | |
| Methodologies | |
| Agile ( XP , Lean , Scrum , FDD , etc.) • Cleanroom • OpenUP • RAD • RUP • MSF • DSDM • TDD • BDD | |
| Related disciplines | |
| Configuration Management • Project Management • Requirements Management • Quality Assurance |
Model Content
In 1970, in his article, Royce described as a concept what is now called the "cascading model", and discussed the shortcomings of this model. There he showed how this model can be modified to an iterative model.
In the initial cascade model, the following phases went in this order:
- Definition of requirements
- Design
- Construction (also “implementation” or “coding”)
- Embodiment
- Testing and debugging (also “ verification ”)
- Installation
- Support
Following the cascade model, the developer moves from one stage to another strictly sequentially. First, the “requirements definition” phase is fully completed, resulting in a list of software requirements. After the requirements are fully defined, there is a transition to design, during which documents are created that describe in detail for programmers the method and plan for implementing these requirements. After the design is fully completed, the programmers carry out the implementation of the resulting project. The next stage of the process is the integration of individual components developed by various teams of programmers. After the implementation and integration are completed, the product is tested and debugged; at this stage, all the shortcomings that appeared at the previous stages of development are eliminated. After that, the software product is implemented and its support is provided - introducing new functionality and eliminating errors.
Thus, the cascade model implies that the transition from one development phase to another occurs only after the complete and successful completion of the previous phase, and that there is no transition back or forward or overlapping phases.
Nevertheless, there are modified cascade models (including the model of Royce himself) that have small or even significant variations of the described process.
Cascade Model Criticism and Hybrid Methodological Decisions
The “Cascade Model” technique is often criticized for lack of flexibility and the end in itself formal project management at the expense of time, cost and quality. Nevertheless, when managing large projects, formalization was often of great value, as it could drastically reduce many project risks and make it more transparent . Therefore, even in the PMBOK version 3, only the “cascade model” methodology was formally fixed and no alternative options known as iterative project management were proposed.
Since PMBOK version 4, a compromise has been reached between methodologists committed to formal and progressive project management with methodologists who rely on flexible iterative methods . Thus, since 2009, formally, the Institute for Project Management (PMI) has proposed both a standard hybrid version of the project management methodology, combining both the advantages of the Waterfall methodology and the achievements of iterative methodologists.
See also
- Flexible development methodology
- Iterative development
- Spiral model