The waterfall model originated in manufacturing and construction where changes are costly and investment in design of the production line is often much less than potential loss if the actual production fails. It is based on idea that planning and design costs are much lower than those used in the actual production.
## Software development life-cycle (SDLC)
The software waterfall model often uses some variation of following phases:
- Requirements specification (Requirements Analysis) resulting in Requirements Document
- Software design resulting in Software Design (SD) document
- Implementation resulting in the actual software
- Testing (or Validation)
- Deployment (or Installation)