01Overview
In 1970 Royce drew the “waterfall” in a paper: each phase completes before the next begins, with backtracking where needed. He himself argued for iteration, but the simplified diagram was widely adopted and became the standard process of governments and large enterprises.
Waterfall suits projects with stable requirements and heavy compliance, and struggles with uncertainty. Document-driven stage gates make change expensive, and users often see the product only at the end. The spiral model of the 1980s and the iterative methods of the 1990s were corrections. Waterfall never disappeared; it now appears mixed with agile in aviation, medical and infrastructure software.
02History
- 1970
Royce's waterfall paper
The classic statement of staged process.
- 1970
The SDLC spreads
The software lifecycle becomes a management framework.
- 1986
The spiral model
Boehm introduces risk management.
- 2001
The Agile Manifesto
A reaction against document-heavy process, written at Snowbird.
03Core concepts
Lifecycle
The division into phases from requirements to maintenance.
Stage gate
A review and a set of deliverables at the end of each phase.
Requirements freeze
Requirements locked before development, assuming change is expensive.
04Hands-on
Do it once — it beats reading it ten times
Write a one-page plan for a small feature in waterfall style, then rewrite it as two-week iterations; note what became unknowable
05Self-check
Say it in your own words first, then open the answer. Whatever you cannot explain is what to review next.
Can you explain "Lifecycle"?
The division into phases from requirements to maintenance.
Can you explain "Stage gate"?
A review and a set of deliverables at the end of each phase.
Can you explain "Requirements freeze"?
Requirements locked before development, assuming change is expensive.
What problem did it solve, and why was there nothing better at the time?
Go back to the history section: how was this done before, and what did it cost?
If you had to build it today, how would you break it down?
Use the hands-on task above: write a plan of at most three steps before you start.
06Key people
Winston Royce
1929 – 1995
Formulated the waterfall model.
Barry Boehm
1935 –
The spiral model and software economics.
07Further reading
- Managing the Development of Large Software Systems
- Software Engineering Economics