Waterfall: the Plan and Document approach
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It is called the waterfall model because each phase occurs one after the other. It is called the Plan and Document perspective because before writing code we come up with a plan for the project, including extensive, detailed documentation of all the phases, and progress is measured against this plan.
EXAMPLE 2 months for requirements + 3 for design + 4 for development + 3 for testing = 12 months. At release the client says "I don't like it!!". There may have been a misunderstanding about the requirements, the client may have changed their mind about some requirements, or they may not like the user interface — so the team must go back, refine the requirements and start the process again.
Four drawbacks of the waterfall model
1. Increase in cost and time if changes are required later on.
2. Clients may not know what they need — they might need to see something first.
3. Developers/designers may not know which design is most feasible or usable by clients.
4. Quite long — usually 6–18 months for one cycle.
REMEMBER Waterfall = plan and document the phases, with a risk of discovering problems late.