[28 June 2010]
Many people have been influenced by what is often called Postel’s Law, usually quoted as saying “Be conservative in what you send and liberal in what you accept”.
In a room with a whiteboard, however, the only workable rule is: when you find a marker that no longer writes, do not be liberal in what you accept, and do not put it back where you got it. Throw it away. Otherwise, every whiteboard you run into will soon have twenty-odd markers, some of which actually work, if you can find them, but most of them duds.
Cleaning up as you go is a good principle in cooking, and in managing the set of white-board markers. It’s also a good idea in data management; it’s a shame so many people misread Postel’s Law to mean the opposite.
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My new job involves handling a lot of clinical data. I’ll be interested to see how this plays out in that context.
Quite right about the WMR, which also applies to pens in a pen jar. I’ll take this opportunity to explicate Postel’s Law a bit, though: It does not mean “Accept any old crap and try to make sense of it” (a la HTML5); it means “Handle all the valid corner cases yourself, but don’t assume that people downstream of you can necessarily handle them.”
I’ve been in the business since the mid-70’s and (shock!) only heard of Postel’s law today. How does this add to Claude Shannon’s work from the 40’s?
Specifically, what would one do (picking on the XML battle) if the last closing bracket was missing from an otherwise well formed document? If rejection is the answer, then one denies entropy.
John, thanks for the comment.
An XML processor is obligated to report that a data stream missing the final closing bracket is not well formed. I think that’s not so much denying entropy as acknowledging that it may have two sources which are usefully distinguished: the information in the message is worth preserving, but the noise introduced by errors in transmission has a different origin and should not be confused with message content.