Saturday, 18 May 2013

Second order poka-yoke

Poka-yoke is the practice of "mistake-proofing" - designing interfaces in ways that prevent users from making mistakes.

Continuous integration is a form of poka-yoke for software development. Developers are prevented from releasing (obviously) broken software to production by a battery of tests.

However, poka-yoke is about designing to mitigate specific user mistakes (at least as I understand Shingo's definition). In other words, it's about putting up safety barriers between users and anticipated failure modes.

How much better to develop in a software ecosystem that discourages not only the occurrence of mistakes, but encourages the growth of designs that do not admit the possibility of these mistakes.

My colleague Gurpreet Luthra cites the example of making heat-resistant bolts a different size to ordinary ones so that they cannot be accidentally interchanged. However, were the design to be simplified so that the engine was a single piece of metal, bolts would not be required at all.

Sometimes simplification is possible. Other times essential elements of the domain force us to introduce scope for error. Perhaps engines could be constructed differently to simplify assembly. Perhaps not. The only way to tell the difference is to be constantly vigilant for the possibility of eliminating accidental complexity.

Having thorough test coverage is good. Preventing the complexity that disrupts developers' ability to comprehend the system well enough to avoid mistakes is better.

Simple designs can not only make mistakes avoidable, they can make them literally inconceivable. By that construction, you could consider a disciplined pursuit of simplicity second-order poka-yoke.

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