SAX2 Namespace Support

[David Megginson]

Hunter, David writes:

 > > > The problem though boils down to how often, in reality, XML
 > > > instances will have the same Namespace declared twice, with
 > > > different prefixes.
 > > 
 > > The fact that the bug would be rare makes it worse -- an
 > > application will run perfectly for, say, 18 months, then will
 > > suddenly and inexplicably blow up long after the original
 > > programmers have moved on because one input document happened to
 > > declare the same NS twice and the programmers didn't build in
 > > error recovery for that problem.
 > 
 > I don't want to flog any dead horses, so I hope this hasn't been covered
 > already, but is it really an error to have the same namespace declared
 > twice, with different prefixes?  

No, it's not an error at all.  We're concerned about the borderline
case where there are two QName objects

  {"http://www.w3c.org/1999/xhtml", "p", ""}
  {"http://www.w3c.org/1999/xhtml", "p", "html"}

and a program compares them with equals() in Java or == in C++.  Most
people are arguing that the two should be equals()/==, but a few
people have pointed out that that is a nasty trap for any programmer
who is not extremely familiar with the Namespaces spec.

My proposed solution is simply to punt: don't introduce a QName class
in SAX2, and leave such things to higher-level specs, which can
deal with these as they see fit.


All the best,


David

-- 
David Megginson                 david at megginson.com
           http://www.megginson.com/

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