Waterfall model of software development

The waterfall model (also called the cascade model) is one of the earliest and simplest approaches to the software development lifecycle. The development process is broken down into several phases, each of which follows strictly after the previous one, with no going back to earlier stages.

In other words, development flows like a "cascade" or "waterfall" from top to bottom, from one phase to the next.

Key principles of the model

1. The move from one development phase to the next happens only after the previous phase is fully and successfully completed. For example, you can't start writing code without a fully approved design, or begin testing while some modules are still unfinished;
2. Strict project documentation. Each development phase is described in detail in the project documentation. The waterfall model is characterized by strict adherence to the plan;
3. A rigid sequence of phases. The waterfall model does not allow skipping phases or returning to previous ones;
4. Any changes must be agreed with the customer and documented;
5. Testing and bug detection happen only after development is complete;
6. Once the requirements specification is approved, the customer does not take part in building the product.

Phases of the waterfall model

The classic software development model includes the following phases:

1. Planning In this phase, a detailed project plan is developed. Timelines, budget, resources, and tasks are defined. The phase includes forming the development team, assigning responsibilities and creating a work schedule.
2. Requirements analysis In this phase, the requirements for the software product are gathered and documented. It involves talking with the customer and end users to understand their needs. The result of this phase is a requirements document.
3. Design In this phase, the architecture of the software product is developed. Data structures, user interfaces, system components, and algorithms are designed. The phase also includes designing the user interface (UI) and defining technical specifications.
4. Development At this point, active coding begins. Developers write the program according to the requirements and design defined in the previous phases. Development may include building various modules, components and functional parts of the program.
5. Testing and deployment In this phase, the quality of the software product is verified through various types of testing, including unit, integration, functional, and other tests. After testing, the software is released to production. It is installed on the target server or distributed to end users.
6. Support After release, the software continues to be maintained and updated. This phase may include rolling out updates, fixing bugs as they arise, providing technical support to users, and responding to requests to change or add functionality.

The waterfall model provides a clear, easily managed development process. Phases are carried out sequentially, which makes it easier to control the project lifecycle;

Transparency. The entire development process is presented as clear phases, which makes the project transparent for both developers and customers;

Fixed requirements. Project requirements are clearly defined at the start, which prevents changes during development;

Project documentation. Detailed documentation is produced at every phase of development, which helps with subsequent maintenance and support of the software product.

Changes are hard to make. Because of its linear structure, the waterfall model can be ineffective when you need to respond quickly to changes in requirements after development has started;

Long development cycle. Since each phase is carried out sequentially, the process can take a long time, and the customer won't see results until the entire project is finished;

Limited interaction with the customer. The client may see results only after the project is complete, which reduces opportunities for feedback and real-time adjustments.

When to use the waterfall model

The waterfall model is gradually losing popularity to more flexible iterative models. Even so, the classic waterfall approach is still in demand in some scenarios.

Besides the waterfall model, there are several alternative software development models:

• Agile model (agile development methodology) Agile is based on iterative and incremental approaches, with an emphasis on constant close collaboration with the customer, readiness for change, and frequent delivery of working software. The model involves adaptive planning and the ability to respond quickly to changing requirements.
• Spiral model Involves phased development with mandatory risk analysis at each iteration and the ability to return to previous phases. It stands out for its support of an iterative approach and its focus on risk assessment.
• V-model A strict sequence of phases, as in waterfall, but with an emphasis on verifying and testing each phase against the outputs of the previous one. A more formalized approach than the waterfall model.
• RAD (rapid application development) Based on shortening development time through prototyping and intensive customer involvement. The model focuses on quickly building working versions of the software.

How the waterfall model differs:

1. Linear approach The waterfall model uses a linear, sequential development method in which each phase depends strictly on the previous one. This structured, sequential execution of phases sets it apart from other models.
2. Limited flexibility Unlike other models, the waterfall model does not allow for flexible responses to changing requirements during development.
3. Clear structure One of the advantages of the waterfall model is its clear structure, which makes the project easy to manage, especially when requirements are well defined in advance.
4. Focus on the end result Unlike iterative models, which focus on step-by-step improvement, the waterfall model concentrates on fully completing each phase before moving on to the next.