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   Re: parser for xml-data?

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  • From: Paul Prescod <papresco@technologist.com>
  • To: xml-dev@ic.ac.uk
  • Date: Sun, 24 May 1998 14:17:22 -0400

Charles Frankston wrote:
> The ns pseudo-attribute is NOT supposed to be a URL.  It's a URI.  

In the absence of any way to actually use URNs, the difference does not
strike me as relevant. My point was that your example was misleading
because it didn't use something that looked like either a URL or a URN.

> Something like a URN or
> a UID would frankly make a better ns ID.  We just don't yet have good
> mechanisms deployed for doing the lookup from the URN or a UID to find the
> identified schema (if indeed you actually need a schema).  I think once we
> define this, it would be better to avoid using URLs for the purpose of
> uniquely identifying names.

I agree. In fact, once URNs are deployed it will also make sense to use
them for hypertext links, graphic embedding and everything else. But they
aren't. For now, I'm not sure why you would argue that URLs are
inappropriate. There is nothing better, for namespaces, hyperlinks or any
other use.

> In order to use these DTDs you wrote, I MUST use the prefixes you chose for
> your instance.  Your ns part, which probably should really read something
> like ns="urn:schemas-abc-com:zyx" is now useless.  

No it is not. It locally binds a short name in the document's namespace to
a longer name in a globally managed namespace.

> If I want to use your
> DTDs and mix them with any other DTDs, I must ensure that the other DTDs do
> not in fact also use any "zyx" or "xyz" prefixes.  

Authors have the option of copying the other DTD to their sites and
changing the prefix it uses. Then the namespace declaration points back to
the original URI so that software can recover the original, fully
namespace-qualified name. I do not claim that this is convenient or
elegant, but the namespace proposal was explicitly designed to support
it...which is why you can use namespaces without using ANY. Actual prefix
collisions requiring this operation are likely to be rare.

 Paul Prescod  - http://itrc.uwaterloo.ca/~papresco

Guns don't kill people. Children kill people.

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