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Clarification on xsl:attribute requested

From: Rick Jelliffe <ricko@topologi.com>
Date: Thu, 27 Jun 2002 04:37:10 -0400 (EDT)
Message-ID: <01a401c21db7$a80f2260$4bc8a8c0@AlletteSystems.com>
To: <xsl-editors@w3.org>




A recent version of Xerces acts differently w.r.t. namespaces compared
to other implementations of XSLT.  While I believe it is a bug, and we
are reporting it, I think the XSLT specification should be clarified to
prevent future occurrences of this problem.

The bug was reported by a user of Schematron who had namespace
problems.

XSLT prevents namespaces being added dynamically using 
<xsl:attribute name="xmlns" namespace="blah" />

But Schematron (and programs like it) require a mechanism
for dynamically setting namespaces, because these are sourced
from a schema not from a stylesheet. 

So the Schematron language provides an element
 <sch:ns prefix="blah"  url="blahblah"  />
which is converted to 
<axsl:stylesheet>
 <xsl:attribute name="concat(@prefix, ':dummy-namespace-attribute')"
    namespace="@url" />
...

According to the XSLT spec the output <xsl:stylsheet
 1)   should have an attribute  XXX:dummy-namespace-attribute="" 
 2) should have a namespace declaration  xmlns:XXX="blahblah"

Xerces fails in this, and I think it needs to be clarified that 
a namespace should be generated.

Now, as an extra wrinkle, the namespace spec does mention
that we cannot guarantee that the same prefix will be used.

However, except for Xerces (which does not get up to
that stage) all implementations of XSLT that I have tried
do preserve that prefix, so we get the desired
   <xsl:stylesheet  blah:dummy-namespace-attribute="" xmlns:blah="blahblah">
which then allows the prefix to be used in the XPaths and expressions
that are generated.

So I would ask that this behaviour (which is standard) also be clarified,
to help any system that needs to dynamically create namespaces.

To summarize what I would like in an XPath erratum:

1) Clearer exposition that you may have to generate a namespace
declaration for an <xsl:attribute which supplies its own namespace
attribute.  And that if the Qname has a prefix, the namespace
declaration needs to be generated with an appropriate prefix
too.  (I believe this is what the current spec implies, and it
is how most implementations work, and it is hard to see how
else it could work.)

2) Wording to the effect that if a namespace is used with only
a single prefix in a document, that prefix *should* be the one
used in any output XML.    (Whether this can be overriden
by user option, or what happen if the same prefix is bound to 
different namespaces or if the same namespace is bound to multiple
prefixes are all issues that I do not think require clarification,
as they are outside my requirement.)

I believe this clarification merely reflects common practise
and common sense.   It does not enshrine the prefix, but
merely says "if the user has specified a prefix, you may
as well use that rather than making up an arbitrary one."

Cheers
Rick Jelliffe
Received on Thursday, 27 June 2002 04:53:54 GMT

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