xml-dev - Re: namespace prefixes within attribute values

[David Megginson <david@megginson.com>]

Ray Whitmer <ray@xmission.com> writes:

> Perhaps I missed something, but would this type of value become
> shredded if you save canonical XML, which reassigns all the prefixes
> but presumably does not know about namespaces in values represented
> by prefixes?
> 
> Is that a problem?

Yes, a very big one (and, I think, the main reason for Tim's
opposition).  Consider the following document:

  <doc:doc xmlns:doc="http://www.acme.com/doc/">
   <doc:thing1 foo="doc:x" bar="doc:y"/>
  </doc:doc>

How can a general-purpose transformation engine know, for example,
that "doc:" in the 'foo' attribute value is meant to be a Namespace
prefix and the "doc:" in the 'bar' attribute value is not?  If I
change the prefix to "xxx", I might want

  <xxx:doc xmlns:xxx="http://www.acme.com/doc/">
   <xxx:thing1 foo="xxx:x" bar="doc:y"/>
  </xxx:doc>

or

  <xxx:doc xmlns:xxx="http://www.acme.com/doc/">
   <xxx:thing1 foo="doc:x" bar="xxx:y"/>
  </xxx:doc>

or

  <xxx:doc xmlns:xxx="http://www.acme.com/doc/">
   <xxx:thing1 foo="doc:x" bar="doc:y"/>
  </xxx:doc>

or

  <xxx:doc xmlns:xxx="http://www.acme.com/doc/">
   <xxx:thing1 foo="xxx:x" bar="xxx:y"/>
  </xxx:doc>

and there's no way to tell except through the relatively expensive
path of consulting a schema.  While it's annoying for typists, it's
generally a lot more robust to have

  <doc:doc xmlns:doc="http://www.acme.com/doc/">
   <doc:thing1 foo="http://www.acme.com/doc/x" bar="doc:y"/>
  </doc:doc>

At least now I can tell what's meant without a schema.


All the best,


David

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

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