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Simon St.Laurent wrote:
> This has come up before, but the chant "Postel's law has no exceptions"
> seems to be coming again, in the RSS context.
>
> http://tbray.org/ongoing/When/200x/2004/01/11/PostelPilgrim
>
> has Tim Bray's argument and lots of links to others.
>
> Norm Walsh also has a piece at:
>
> http://norman.walsh.name/2004/01/12/postel
>
> Also an interesting bit at:
>
> http://www.intertwingly.net/blog/1685.html
I think part of the problem are different interpreations about what the
law actually is about. Very good summary by Ed Davis on
<http://norman.walsh.name/2004/01/12/postel>:
> There are two interpretations of Postel's Law: the conservative and the liberal. The conservative interpretation is that if there is an ambiguity in a specification then you should:
>
> 1. Be careful not to produce data whose compliance is ambiguous.
>
> 2. Be careful to accept any data which might reasonably be considered to comply with the specification.
>
> Also, maybe you should fix the specification.
(I'll add: excepting broken messages doesn't necessarily mean that they
should silently be accepted, it just means that the recipient should act
in a predictable way).
> The liberal interpretation of Postel's Law is that even data streams which unambiguously do not comply with the specification should be accepted.
>
> I'm fully in favour of the conservative interpretation but I think anybody who supports the liberal interpretation rather misses the point of having a specification in the first place.
Needless to say, I'm convinced that application of the "liberal"
interpretation actually *causes* interoperability problems (a recently
shown by the experiment done here:
<http://www.intertwingly.net/blog/1685.html>).
I'll also note that both the W3C ([1]) and the IETF (as far as usage of
XML in protocols is concerned, [2]) seem to favor a conservative approach.
Julian
[1] <http://www.w3.org/TR/webarch/#no-silent-recovery>
[2] <http://greenbytes.de/tech/webdav/rfc3470.html#rfc.section.4.1>
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