The Waterfall model is originally invented by Winston W. Royce in 1970. He wrote a scientific article that contained his personal views on software development. In the first half of the article, he discusses a process that he calls “grandiose”. He even drew a figure of the model, and another showing why it doesn’t work (because the requirements always change). This model is the waterfall. He used it as an example of a process that simply does not work. In the latter half of the article he describes an iterative process that he deems much better.
OK, so why do people still advocate the waterfall? If you look at the scientific articles on software engineering that discuss the waterfall, they all cite Royce’s article. In other words, they’re saying something like “The waterfall is a proven method (Royce, 1970).” So they base their claims on an article that actually says the opposite: that the model does not work.
This is how science (unfortunately) often works – researchers just cite something, because everyone else does so as well, and don’t really read the publications that they refer to. So eventually an often cited claim becomes “fact”.
Agile methods and the linear method were both originally used already in the 1950’s. The scientific mis-citing boosted the waterfall’s popularity, but in the 1980’s it was being phased out – because people had found out (the hard way) that it does not work.
But, things change as a busy engineer in the US defense organization is asked to come up with a standard for military grade software projects. He doesn’t know what a good process would be, and he’s told that “Hey, Royce already came up with the correct method: the waterfall. Use it.” So the waterfall becomes the US military standard DoD-2167.
A bit later the NATO countries notice that they too need a software engineering standard. And they ask the US for their standard – no need in reinventing the wheel, right? And thus the waterfall is again used everywhrere, since if the military uses it, it must be good. Right?
Here in Finland we had already dropped the waterfall in the 1980’s, but after the DoD-2167 was sent over the Atlantic like a weapon of mass desctruction, it became the standard, again.
What have we learned here: The agile (iterative, incremental) methods are not new. They’re as old as the waterfall. There is no scientific evidence that the waterfall works – on the contrary, most projects fail. There is, however, massive evidence that agile methods improve productivity, quality and success rates.
So what should we really have learned: People remember images. And people often read the beginning of an article, but not the end.
So: Don’t draw figures or diagrams of wrong models, because people will remember them. And in the worst case that could cause hundreds of thousands of failed projects and billions of euros and dollars wasted for nothing.
Update (February 2010): Commenters have been asking for references to back up my claims, so I added links to the most central documents referred in this blog post.