Waterfall approach

Software development has gradually evolved from unstructured to structured, both in producing programs and in managing projects

The waterfall approach assumes all requirements are written down before producing them. Each definition is "signed off" by the user before starting work

Project definition signed before starting project
Systems analysis agreed before starting design
Design agreed before starting programming, and so on

Advantages: Planned duration, responsibility pinned down, orderly, should result in few corrections late in project

Waterfall approach

All is not rosy

It can be difficult to state when a stage is complete, ie. we may have to correct to previous work

Causes of failure once a project has started:

74% Unclear objectives and requirements
60% Lack of business commitment
58% Business requirements changing
45% Poor communication
- Taylor A (2000) IT projects: sink or swim, Computer Bulletin January 2000, BCS
"No-one knows what they want until you give them what they ask for" (Gerry Weinberg)

Alternative approach: Rapid Application Development (RAD)

Closely associated with prototyping
though prototyping can be used in both waterfall and RAD projects