Namespaces and XML validation

[David Megginson]

Charles Frankston writes:

 > I do not believe the new namespace proposal with local scoping
 > makes [DTD validation] any harder to do than the old PI based
 > namespace proposal. 

This claim is incorrect, though the culprit is the local scoping and
defaulting rather than the declaration mechanism itself.

XML 1.0 DTDs know only about one-part, unresolved names (i.e. "foo" or
"bar:foo", not null + "foo" or "http://www.megginson.com/" + "foo").

Without local scoping and defaulting, there was still guaranteed to be
a one-to-one relationship between unresolved names and resolved
(two-part) names, and thus, only one XML unresolved name for each
element type and one element type for each name; as a result, it was
possible to write a DTD for _any_ document that used namespaces.

With local scoping and defaulting, there is a many-to-many
relationship between unresolved names and resolved names, and thus,
possibly more than one XML 1.0 name for each element type and more
than one element type for each name.

Tim has rightly pointed out that DTD validation is possible only on a
small subset of the documents allowed by the new spec -- that is,
documents use only one unresolved name for each element type and one
element type for each unresolved name.  He also rightly points out
that any XML document can be mechanically transformed so that it
belongs to this subset.


All the best,


David

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

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