Re: [xml-dev] RE: Application of Postel's Principle to XML

[Michael Kay <mike@saxonica.com>]

On 16/02/2013 22:02, Costello, Roger L. wrote:

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Hi Folks,

 

I recently came across this statement in a requirement's document:

 

Verify using XPath that there are no elements or attributes

in an XML document with more than X amount of characters.

 

That seemingly simple requirement has ambiguities that senders and receivers must wrestle with. Here are the ambiguities:

 

1. Does "X amount of characters" include whitespace?

2. Can the XML contain mixed content?

Yet another irritating question from Roger, which like most of his others will probably lead to an interesting discussion.

First the irritation -

(a) what on earth is the point of posting an absurdly imprecise requirements statement and then telling us it's imprecise? Of course it is, so what?

(b) Postel's law has nothing to do with how you deal with an imprecise specification. It assumes that the specification is clear, and suggests that you don't insist that your input conforms to it.

Michael Kay
Saxonica

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