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   re: illegal namespace usage

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  • From: "Dean Roddey" <droddey@charmedquark.com>
  • To: <xml-dev@ic.ac.uk>
  • Date: Sun, 15 Aug 1999 19:02:53 -0700

>Simon St.Laurent wrote:
>> I've concluded that namespaces itself is a great idea.  I've also
>> that integrating it with XML 1.0 in any reliable way is pretty much
>> impossible.
>Please explain this statement.

I agree with Simon. Here's an example:

If you are validating, then all attributes used by an element must be
defined as legal attributes for that element. However, that's totally in
conflict with what namespaces are supposed to be for. If I have to predefine
xmlns:foo, then you *have* to use foo as the prefix. But the prefix is
supposed to be up to you (i.e. its not important, only what it maps to is
important.) To me, this is a pretty bad conflict. I'm currently of the
opinion that the validation should skip them except to check (if they are
defaulted or fixed) that they have the correct predefined value. Am I
missing something on this front?

And, if you decide that you don't force them to be predefined, do you tell
the application about them? If you don't force them to be defined, then they
are really just infrastructure and not part of any content model. If you
then pass them to the app, it has to explicitly skip over them (more
overhead.) If you don't, then it cannot recreate the document.

And of course there are all the issues with DTDs that are really bad. About
half the time you deal with them lexically and half the time logically,
which is not good for anyone.

And Schema introduces some other issues, such as:

1) You scan a start tag QName
2) YOu scan the attributes for xmlns attributes and update your namespace
3) You then look up the element in the pool via its {uri}name.
4) Then you find out that it defined an xmlns attribute that would have
mapped its own prefix to something different.

This is a catch-22 that cannot be gotten around if you follow the namespace
rules (which allows an element's attributes to affect its prefix) and the
XML 1.0 rules (which allows for fixed or defaulted attributes.) Some have
argued that Schema is a non-issue since its not XML 1.0 and therefore it
cannot default/fix attributes, but certainly that functionality looks to be
part of the Schema spec if it is going to reasonably be used in many places.

Dean Roddey
The CIDLib Class Libraries
Charmed Quark Software

"100% Substance Free. Less Content, more cost. Just the way you like it"

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