Waterfall Model

The waterfall model is the classic model of software engineering. This model is one of the oldest models and is widely used in government projects and in many major companies. Because the model emphasizes planning in the early stages, it catches design flaws before they develop. Also, because the model is document and planning intensive, it works well for projects in which quality control is a major concern.

The pure waterfall model consists of several non-overlapping stages, as shown in the following illustration. The model begins with establishing system requirements and software requirements and continues with architectural design, detailed design, coding, testing, and maintenance. The waterfall model serves as a baseline for many other life cycle models.

The following list details the steps for using the waterfall model:

• System requirements—Establishes the components for building the system, including the hardware requirements, software tools, and other necessary components. Examples include decisions on hardware, such as plug-in boards (number of channels, acquisition speed, and so on), and decisions on external pieces of software, such as databases or libraries.
• Software requirements—Establishes the expectations for software functionality and identifies which system requirements the software affects. Requirements analysis includes determining interaction needed with other applications and databases, performance requirements, user interface requirements, and so on.
• Architectural design—Determines the software framework of a system to meet the specified requirements. The design defines the major components and the interaction of those components, but the design does not define the structure of each component. You also determine the external interfaces and tools to use in the project.
• Detailed design—Examines the software components defined in the architectural design stage and produces a specification for how each component is implemented.
• Coding—Implements the detailed design specification.
• Testing—Determines whether the software meets the specified requirements and finds any errors present in the code.
• Maintenance—Addresses problems and enhancement requests after the software releases.