Waterfall is a linear approach to software development. In this methodology, the sequence of events is something like:
- Gather and document requirements
- Design
- Code and unit test
- Perform system testing
- Perform user acceptance testing (UAT)
- Fix any issues
- Deliver the finished product
In a true Waterfall development project, each of these represents a distinct stage of software development, and each stage generally finishes before the next one can begin. There is also typically a stage gate between each; for example, requirements must be reviewed and approved by the customer before design can begin.
Developers and customers agree on what will be delivered early in the development lifecycle. This makes planning and designing more straightforward.
Progress is more easily measured, as the full scope of the work is known in advance.
Throughout the development effort, it�s possible for various members of the team to be involved or to continue with other work, depending on the active phase of the project. For example, business analysts can learn about and document what needs to be done, while the developers are working on other projects. Testers can prepare test scripts from requirements documentation while coding is underway.
Except for reviews, approvals, status meetings, etc., a customer presence is not strictly required after the requirements phase.
Because design is completed early in the development lifecycle, this approach lends itself to projects where multiple software components must be designed (sometimes in parallel) for integration with external systems.
Finally, the software can be designed completely and more carefully, based upon a more complete understanding of all software deliverables. This provides a better software design with less likelihood of the �piecemeal effect,� a development phenomenon that can occur as pieces of code are defined and subsequently added to an application where they may or may not fit well.