Mythical Man-Month: Planning for Change
December 11, 2011
Part four in a series. In the chapter titled "Plan the System for Change," Dr. Brooks again lays out the foundations for Agile software development. His was an era of dumb-terminals and highly scheduled availability. And yet, here he is saying, "plan to throw one away; you will, anyhow." When RAM wasn't cheap, and good programmers even more rare than today, how does a project manager or architect justify throwing out the first design on purpose? By recognizing that "[t]he only question is whether to plan in advance to build a throwaway, or to promise to deliver the throwaway to customers."
This followed an analogy to the creation of a physical pilot plant for testing out a proposed manufacturing design. That sounds to me like a prototype. Spend an early iteration on a quick-and-dirty prototype of your design, run it by the users, and incorporate the feedback into a fresh implementation. But it does seem to miss the beauty of refactoring: get it working, then clean it up. Perhaps the refactoring concept did not work as well in those green-screen, procedural days, before you could re-compile every few minutes.
It is not sufficient, Brooks posits, to expect changing requirements and hope for the best. Thus he goes on to advocate that the software development group be organized for success in a changing environment. But he also makes the assertion that software needs more control, not less, which on the surface seems to be a call for a strict waterfall. He doesn't want tentative plans.
One of the signs of true genius is recognizing new data, accepting that a former conclusion might be wrong, and moving forward with the new premise. In new chapter "The Mythical Man-Month after 20 Years," Brooks accepts that "[t]he biggest mistake in the "Build one to throw away" concept is that it implicitly assumes the classical sequential or waterfall model of software construction." Thus in 1995 his vision of software development was updated to include the reality of incremental and iterative design. His 1986 paper, "No Silver Bullet" (ch 16) actually spelled out the need to "[utilize] rapid prototyping" and "[grow] software organically." A common misconception about Agile development is that it is uncontrolled. In the context of the whole, Brooks is calling for careful governance without the stultifying commitment to tollgates and a single-pass design that are called for by waterfall.
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