How about over 1,000,000 XHTML Namespace URIs?

Wed Sep 1 23:33:33 BST 1999

Hunter, David writes:

 > In other words, any application which is working with XML can just
 > look for that namespace and say "oh, this element is using XHTML.
 > I'll hand it off to the XHTML application to process".  If we use
 > separate namespaces, then any application which may have XHTML to
 > process will have to know about all of those namespaces.  Perhaps
 > not a big deal, if only those three namespaces are ever used, but
 > perhaps a huge deal if more flavours of XHTML are created, or the
 > namespaces are versioned.

In fact, there could end up being an exponential explosion of
XHTML-related Namespaces, depending on how the HTML WG intends to
proceed (it's not explicit in the publicly-available XHTML documents,
and I hear contradictory things from the WG members).

What happens when a vendor wants to create a new element that will
appear in, say, an HTML paragraph?  Obviously the new element itself
(such as <ms:spreadsheet> or <ra:videoclip>) will have to be in a
different Namespace -- that's the whole point -- but will the
containing paragraph have to be in a different Namespace as well?  In
other words (assuming that XHTML is the default Namespace) can we have

  <p>Today, President Clinton visited the finger lakes.
    <ra:videoclip src="clinton.ram" />.</p>

  <p>Economic indicators are down.
    <ms:spreadsheet src="stuff.xls" />.</p>

or does it have to be this?

  <ra:p>Today, President Clinton visited the finger lakes.
    <ra:videoclip src="clinton.ram" />.</ra:p>

  <ms:p>Economic indicators are down.
    <ms:spreadsheet src="stuff.xls" />.</ms:p>

(And, of course, an <ms:li> to hold the <ms:p>, and an <ms:ul> to hold
the <ms:li>, and an <ms:body> to hold the <ms:ul>, and an <ms:html> to
hold the <ms:body> -- it will always necessarily bubble to the top
<html> element).

If the HTML WG takes this (terrifying) path, then what happens when a
Web author wants both extensions in the same paragraph?  <ra:p>
doesn't allow <ms:spreadsheet>, and <ms:p> doesn't allow
<ra:videoclip>, so it looks like she's somehow expected to invent yet
another Namespace herself:

  <my:p>Today, President Clinton visited the finger lakes.
    <ra:video-popup src="clinton.ram" />.  Economic indicators are 
    down. <ms:spreadsheet src="stuff.xls" />.</my:p>

My math sucks, but as far as I can figure out, that means that the
number of possible HTML-related Namespace URIs will end up being not
only three, but about two to the power of the number of parties who
decide to create extensions (and that's assuming that each vendor
creates only a single Namespace).

That means that if only 20 parties create extensions for use in XHTML
documents, we will necessarily end up with over 1,000,000 variants of
the <html> element.

That's an awful lot more than three extra lines of code, whatever the
software infrastructure.

All the best,

David

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

xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev at ic.ac.uk
Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ and on CD-ROM/ISBN 981-02-3594-1
To (un)subscribe, mailto:majordomo at ic.ac.uk the following message;
(un)subscribe xml-dev
To subscribe to the digests, mailto:majordomo at ic.ac.uk the following message;
subscribe xml-dev-digest
List coordinator, Henry Rzepa (mailto:rzepa at ic.ac.uk)