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What Is the Waterfall Model? How Is It Used?

What does the Waterfall model really mean? Have you ever thought about that?

  • The word “Waterfall” is often used in comparison to ‘Agile’ but do people know what they really mean when they compare ‘Agile’ to ‘Waterfall’?
  • I think the word ‘Waterfall’ is one of the most loosely-used words in the English language (the word ‘Agile’ is not far behind).

When people talk about ‘Agile’ and ‘Waterfall’,

  • it sounds like they’re comparing two very specific and well-defined methodologies that are binary and mutually-exclusive opposites of each other
  • However, when you dig into what the words ‘Waterfall’ and ‘Agile’ really mean, you quickly discover that’s a very inaccurate and misleading comparison
What Is the Waterfall Model?

What Does the Waterfall Model Mean?

Strictly speaking, the word ‘Waterfall’ was originally defined in 1970 by Dr. Winston Royce in his very famous paper:

Dr. Winston Royce’s 1970 Waterfall Paper

Dr Royce described a model that consists of a sequence of phases. In this model, the outputs of one phase flow into the next phase like a “Waterfall”:

What Is Waterfall

The process was called ‘Waterfall’ because the results of one phase flow into the next phase like a waterfall.

What Was Life Like Prior to the Waterfall Model?

it is useful to understand what life was like prior to Waterfall and what problems it tried to solve. What existed at that time was a lot of poorly-organized development efforts with little or no structure, discipline, and planning. Some of the major problems with the that approach were:

Coordinating Work of Large Development Teams

As projects grew in terms of scope and complexity with potentially much larger numbers of developers, it became apparent that a more planned and structured approach was essential to coordinate the work of large development teams

Cost and Schedule Overruns

The other major problem was that there was very limited predictability over the costs and schedules of software projects:

  • There were many and frequent very significant cost and schedule overruns, and
  • Business sponsors demanded some level of predictability

How Did the Waterfall Model Improve These Problems?

When the Waterfall approach was originally defined, it was a big improvement to go from practically no methodology at all to a very well-defined process. The new Waterfall process provided:

  • A “road map” to:
    • Coordinate the work of multiple developers as well as
    • Integrate the work with any other essential resources outside of the immediate development teams, and
  • A mechanism to gain control over the scope of software projects in order to get more predictability of project costs and schedules

Many younger people today don’t appreciate that history and just criticize Waterfall as being bad without understanding the problems it was intended to solve.

The “Pendulum Effect”

As with many things, there was a “pendulum” effect when the Waterfall approach was initially implemented. There was somewhat of an over-correction in many cases in going from no methodology to a very well-defined methodology. The pendulum swung in many projects from almost no control and discipline to very rigid control and discipline.

It Became Very Rigid and Inflexible

The initial implementation of the Waterfall process had a number of problems that even Dr. Royce recognized in 1970 when he first defined the process. Some of the most serious problems were:

  • The common practice when the Waterfall process was originally defined in 1970 was a very document-intensive and over-controlled process
  • You couldn’t exit a phase until all the documentation required to show that the work required for that phase had been completed, reviewed, and approved
  • The ultimate user of the software didn’t normally even see the software until all of the development and testing was complete and by that point in time; it was very difficult, if not impossible, to go back and make any significant changes
  • The emphasis on control of scope made the process very inflexible to any changes that might be needed to meet user needs and business goals in an uncertain environment

What Was the Impact?

As a result,

  • There have been many situations where the project may have met cost and schedule goals but failed to provide a sufficient level of business value
  • Another major problem was that a heavy emphasis on documentation and other overhead required for reviews and approvals made the whole process bureaucratic and not very cost efficient

It’s important to note that many of the problems associated with “Waterfall” are a result of how it is implemented and not necessarily inherent problems in the methodology itself.

Why Is the Agile versus Waterfall Comparison So Misleading?

A big reason why the typical Agile versus Waterfall comparison is so misleading is that the words “Agile” and “Waterfall” are so loosely-used:

How is the Word “Waterfall” Loosely-used?

Before Agile came into widespread use, many variations on the original Waterfall model were developed to create a more adaptive approach to solve some of these problems.

  • More iterative processes such as the Rational Unified Process (RUP) and a number of variants became widely-used in the 1990’s and early 2000’s
  • There has been a proliferation of a broad range of many different development models such as the Spiral model
  • Some of those have only a very limited resemblance to the original ‘Waterfall’ model as it was defined in 1970.

In spite of this evolution, people still loosely characterize all of those methodologies as ‘Waterfall’ as if it was one specific, unique and well-defined methodology called ‘Waterfall’ and that is not really the case

The common denominator of all the methodologies that people loosely call ‘Waterfall’ is that

  • They emphasize some level of upfront planning and control.
  • The goal is to try to achieve predictability over project scope, costs, and schedules.

For that reason, I think the word “plan-driven” is a more accurate and objective description of what people really mean when they say ‘Waterfall’.

How Is the Word “Agile” Loosely-Used?

The word ‘Agile’ is also loosely used. We all know that ‘Agile’ is not a specific methodology although many people equate ‘Agile’ with Scrum:

  • Scrum is not really a specific methodology, it is really a framework that is intended to be adaptable to a broad range of situations
  • Agile is not really equivalent to Scrum. There are other Agile methodologies such as Kanban

The common denominator of methodologies that people call ‘Agile’ is that:

  • They are flexible and adaptive and
  • Emphasize creativity and innovation in an uncertain environment

rather than:

  • Emphasizing planning and control to achieve predictability with lower levels of certainty.

For that reason, I prefer to use the word “adaptive” instead of the word ‘Agile’ when comparing it to ‘Waterfall’ (plan-driven).

Overall Summary

When people in the Agile community compare ‘Agile’ and ‘Waterfall’, it’s usually in the context of

  • Agile is good and Waterfall is bad and that’s really not accurate and objective.
  • Saying “Agile is better than Waterfall” is like saying “A car is better than a boat” – both have advantages and disadvantages depending on the environment that you are in.

The words “Agile” and “Waterfall” are very loosely used in practice and that causes a lot of confusion. They are used as if both “Agile” and “Waterfall” are unique, individual methodologies and that is not the case.

The word “Waterfall”, in particular, is very loosely-used.

  • When people use the word “Waterfall”, they’re not necessarily talking about the real “Waterfall model that was defined by Dr Winston Royce in the 1970’s
  • They’re really talking about any plan-driven methodology that is not completely agile.

A better way to think about “Agile” versus “Waterfall” is in terms of “adaptive” versus “plan-driven”. That’s a much more accurate and objective way of making that comparison.

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Additional Resources

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