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   RE: [xml-dev] Postel's Law Has No Exceptions

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> From: Joshua Allen [mailto:joshuaa@microsoft.com]
> Sent: Wednesday, August 20, 2003 7:46 PM
> To: Julian Reschke; Simon St.Laurent; xml-dev@lists.xml.org
> Subject: RE: [xml-dev] Postel's Law Has No Exceptions
> > My point being, unless *everybody* is accepting the same kind of
> broken
> > requests, interoperability will actually be *worse*. But if indeed
> > everybody *is* accepting the same requests, it would have made more
> sense
> Well, I understand the point that Tim makes WRT HTML -- you're not doing
> the client any favors by accepting his buggy input, since it's bound to
> cause him grief later on.  The computing equivalent of "a *real* friend
> would have told me about the kool-aid stains on my shirt!"
> But it seems you are making a different point.  I am saying that WebDAV
> interop issues were not caused by any noble attempts to be "liberal",
> but rather by broken code.  You seem to be responding that "yes, it was
> buggy for the big guy, but then everyone else had to follow suit and be
> liberal to achieve interop".  I can understand this much, but what is
> the conclusion we should draw from this?  What is the relevance to the
> debate about draconian XML processing rules?

None. All I wanted to say is that draconian error checking is very good, and
that it should be used as frequently as possible.

Just recently we had a very weird discussion on the WebDAV mailing list
about a MUST-level requirement for servers where it was suggested that
clients SHOULD handle the case gracefully where the server breaks that
requirement . That's exactly how not to apply Postel's law.

> Are you suggesting that the smaller vendors would have been *better* to
> be draconian?  At first glance, this seems like an issue of "the big guy
> creates defacto standards" rather than something directly related to
> Postel's law.  What am I missing?

Possibly nothing. My impression is that The Robustness Principle is
frequently used as excuse to defend broken implementations. The robustness
principle is *not* about accepting requests that are clearly
malformed/broken/incomplete/whatever -- it is about expecting malformed
requests to come in and behave sanely in that case.


<green/>bytes GmbH -- http://www.greenbytes.de -- tel:+492512807760


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