Sound Engineering and Premature Extrapolation

In a recent post Patrick Logan has a few pointers and quotes about Premature Extrapolation. Henry Petroski’s Design Paradigms: Case Histories of Error and Judgment in Engineering provides a similar perspective, albeit from an angle that has nothing to do with computers.

One of the key messages that Petroski’s book is trying to get across revolves around what Patrick calls premature extrapolations. Paraphrasing Petroski, mediocre engineers scale up designs that worked in the past, hoping that they will also work at a larger scale. Good engineers don’t blindly scale; they start from the other end, analyzing potential failures and then designing to prevent them. One of the many examples he uses to illustrate this point is John A. Roebling’s Brooklyn Bridge (which belongs in the latter category) and Clark Eldridge’s Tacoma Narrows Bridge (which belongs in the former). The book offers many other examples.

I’ve been a fan of Alan Kay’s “Good ideas do not always scale” for many years. I’ve even used it in Chapter 18 of PLoPD4. After reading Petroski’s book I thought that any computer scientist going through it ought to be able to come up with that line.

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