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BizTalk Blog by Chris Han System Design for Enterprise Agility,

Poka-yoke (mistake-proofing) is a technique for mistake-proofing in process design. It's trading the flexibility for less variance. There is a similar concept in software called defensive design or defensive programming.

Yesterday, I just experienced a good example of how important defensive design is. I was trying to plug my external hard-drive to my laptop via USB port. As you know the USB port actually has some sort of defensive design - the connectors in the metal enclosure is actually located only at the lower half. It supposes you can not plug the male connector into it at all if flips it upside down. The problem I see is the implementation of this defensive design on my laptop. The plastic connector is not strong enough to proof a determined idiot like myself. The consequence is serious – the laptop’s power unit is damaged. I guess I have to change the mother board or rather throw away the whole laptop.

Am I too 'Paka' to be a good user? If you use DFMEA method to calculate a Risk Priority Number (RPN) in this case, I'd say hell no. It gets a pretty high score on my calculation:

Severity: 10
Occurrence: 2
Detect and prevent: 5
RPN = S*O*D = 100 

Although it's highly unlikely happens, it is sure one of the failure modes both hard to detect and cause fatal damage. I like the IEEE 1394 (Firewire) socket better at this account. Like at it shape - reduced occurrence; and it's metal - hard to push through. 

 PS. I just realized that USB has a Mini version. It's much closer to 1394's design idea. It's better.

Posted on Tuesday, July 29, 2008 12:48 PM BPM and Enterprise Architecture | Back to top


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