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.