Waterfall model

The waterfall model shows a process, where developers are to follow these phases in order:

• Requirements specification (Requirements analysis)
• Software design
• Implementation and Integration
• Testing (or Validation)
• Deployment (or Installation)
• Maintenance

• Waterfall Methodology

Traditionally, companies have used the Waterfall methodology.  The Waterfall methodology performs each phase of the software lifecycle sequentially:

1. The team creates a list of all requirements before any design is done.
2. Upon requirements completion, a detailed design is created for each requirement.
3. Upon design completion, all tasks are estimated and submitted for approval.
4. Upon approval, coding begins and test cases are created in preparation for quality assurance.
5. Upon code completion, testing begins and continues until all test cases are run and all defects are fixed.
6. Upon quality assurance completion, the software is documented and moved to production.

The advantage of Waterfall is that it is a very disciplined methodology, producing very detailed specifications that can be translated to user and technical documentation. It also provides very detailed oversight, including continual risk management and disciplined project management planning and measurement.
The disadvantage of the Waterfall methodology is that it takes a long time to deliver software to production (normally more than a year). The reason is due to the effort involved in defining all features of the software and creating detailed designs for all of them. It is also problematic because if major flaws are found in the requirements or design, it does not appear until the testing phase, and reworking a flawed design adds risk to the project as well as a lot of effort. Last, because the duration of Waterfall tends to span a year or more, business rules and needs can change, and the original design of the software may not still apply, making features of the new software obsolete before it ever makes it to production

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