Waterfall vs. Agile

I’ve been a fan of Agile methodologies for quite some time now. As an Agilist, I would scoff at the Waterfall process I was taught during my studies. I did read a couple of times that the original paper introducing the Waterfall model wasn’t really supportive of it at all, but I’d never read that paper myself. Until now.

Here’s what I found what its author, Dr. Winston Royce, has to say.

The heart of software development is analysis and coding, “since both steps involve genuinely creative work which directly contributes to the usefulness of the final product.” But for larger software systems, they are not enough. “Additional development steps are required […] The prime function of management is to sell these concepts to both groups and then enforce compliance on the part of development personnel.” The groups mentioned are customers and developers. Wow, not really people over processes, huh?

There are big problems with Waterfall
Royce then goes on to introduce the other steps, ending up with what we now call Waterfall. Right after that he adds feedback loops between each step and its predecessor. The caption to this figure says “Hopefully, the iterative interaction between the various phases is confined to successive steps.” Immediately following that, he points out a problem with this process: “Unfortunately, for the process illustrated, the design iterations are never confined to the successive steps”.

But there is a much worse problem. “The testing phase which occurs at the end of the development cycle is the first event for which timing, storage, input/output transfers, etc., are experienced as distinguished from analyzed. […] If these phenomena fail to satisfy the various external constraints, then invariably a major redesign is required. […] In effect the development process has returned to the origin and one can expect up to a 100-percent overrun in schedule and/or costs.” Yes. Been there, done that.

But these can be fixed
Stunningly, though, Royce goes on to claim “However, I believe the illustrated approach to be fundamentally sound.” We just need to tweak it a bit more: add a preliminary design phase before analysis, document the design, do it twice (he means simulate first, but others refer to this as “plan one to throw away”), look closely at testing, and involve the customer.

And these fixes look a lot like Agile
The first trick to do some design before analysis is also what is common in Agile methodologies. However, we usually don’t single out analysis and design, but apply the trick to all the phases. That’s how we end up with Behavior Driven Development.

Royce turns out to be a big fan of documentation: “In order to procure a 5 million dollar hardware device, I would expect that a 30 page specification would provide adequate detail to control the procurement. In order to procure 5 million dollars of software I would estimate a 1000 page specification is about right in order to achieve comparable control”. Why is documentation so important? One of the reasons is that “during the early phase of software development the documentation is the specification and is the design.” Agilist would rather argue that automated tests are both the documentation and the specification and drive the design. Royce could never have thought of that, since testing in his mind occurred at the end and was to be performed manually.

The do it twice trick is also used a lot in Agile. We call it a spike.

For testing, Royce notices that a lot of errors can be caught before the test phase: “every bit of an analysis and every bit of code should be subjected to a simple visual scan by a second party who did not do the original analysis or code”. Agilists would agree that pair programming is very useful. Also, Royce advises to “test every logic path in the computer program at least once”. He understands it is difficult, but should be done anyway. I agree that we should have (nearly) 100% test coverage, and TDD gives us just that.

For customer involvement, Royce notes that “for some reason what a software design is going to do is subject to wide interpretation even after previous agreement. […] To give the contractor free rein between requirement definition and operation is inviting trouble.” I don’t see how he can maintain this and still be a fan of written documentation. But I am with him in seeing the value of close collaboration with the customer.

So there is no dichotomy
In summary, the author of the Waterfall process clearly saw some problems with that approach. He even identified some solutions that look remarkably like what we do in Agile methodologies today. So why don’t we end this Waterfall vs. Agile false dichotomy and from now on talk just about software development best practices? Make progress, not war.

By the way, what I find amazing is that somehow people managed to get the Waterfall process out of this paper, but not the problems and solutions Royce presented. And it’s almost criminal that the Waterfall process is still taught in universities as a good way to do software development. Without the above fixes, it’s clearly not.


3 thoughts on “Waterfall vs. Agile

  1. Waterfall– rarely do you ever seen waterfall executed in a sequential manner. It is always iterative between the current plane and the one previous. Waterfall doesn’t place quality or scope in the center, a drawback to any modern day approach to development.

  2. I have taken to using the phrase “Single-Pass Waterfall” to refer to the mass misinterpretation of Royce’s paper, to distinguish it from the actual Waterfall that he describes. Irony alert: most organizations learning Scrum start by practising the Waterfall the way Royce intended, albeit with a standard iteration length.

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