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Postel's Rule of Thumb (Was: Postel's law, exceptions)
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In a message dated 1/14/2004 4:59:46 AM GMT Standard Time, elharo@metalab.unc.edu writes:
The original statement of the law comes from section 2.10 of RFC 793
which can be found here:
http://www.ibiblio.org/pub/docs/rfc/rfc793.txt
The actual quote is:
TCP implementations will follow a general principle of robustness: be
conservative in what you do, be liberal in what you accept from
others.
Clearly at the the time Postel meant it to apply only to TCP.
Elliotte,
It is clear that Postel was applying it to TCP. There is no indication either way that he saw its possible "general" relevance as circumscribed to TCP.
It's not obvious to me that he was referring only to spec interpretation
here. Perhaps that becomes clear when this is read in the context of
the whole TCP spec. But whether he meant it or not, the weak form of
Postels' law is a lot more palatable to me than the strong form.
It seems to me that it is a little pompous to elevate a pragmatic and practical design choice by Postel in the specification of TCP to a "law" of supposed universal truth - Postel's Law (sic). Postel put forward an approach which was intended to produce particular practical results in the context of TCP. Postel's so-called "Law" is, in fact, a rule of thumb. It may be applicable outside its originally intended scope. But intelligent assessment of its relevance or otherwise in specific settings with potentially different functional requirements is required. Always remembering that the fifth digit is not the most cogitatively-endowed part of the human anatomy.
Andrew Watt
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