xml-dev - RE: Client recognition of XML Namespace prefixes

[Will Bradley <willbr@microsoft.com>]

Ok, but I'm not using XSLT, I'm using the DOM to access this data, so I
can't just load a schema.  How can I access these nodes from the DOM,
correctly?

Thanks!

-----Original Message-----
From: Clark C. Evans [mailto:cce@clarkevans.com]
Sent: Tuesday, December 05, 2000 6:29 PM
To: Will Bradley
Cc: xml-dev@lists.xml.org; Robert Chen
Subject: Re: Client recognition of XML Namespace prefixes


>   <tree xmlns:dog="http://dogs.com/some/schema"
>         xmlns:people="http://people.com/some/schema">
>     <dog:name>Fido</dog:name>
>
> When a client application recieves this xml block, and wants to 
> interpret it, can it, and should it, make assumptions about the 
> namespace prefix?

The namespace prefix is informational, and thus a
program may make use of the prefix.  However, I would
not make any assumptions about it.  See below.

> How do you find the tag you want within a hierarchy, without knowing 
> what prefix its namespace happens to be using.  It seems that there is 
> no way to be absolutely sure that if I search for "/root//dog:name", 
> another app would not have gone and switched the namespace prefix to 
> "Dog", in which case my search would fail due to case sensitivity, but 
> the XML Validator would NOT fail, because the grammar is still valid.

The stylesheet below should produce the expected result, printing out a line
for each dog's name found.

<xsl:stylesheet version="1.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                xmlns:foo="http://dogs.com/some/schema" > 
  <xsl:template match="/" >
    <xsl:for-each select="//foo:name" >
      I found a dog, named <xsl:value-of select="." />!
    </xsl:for-each>
  </xsl:template>
</xsl:stylesheet>
  

Note that "foo" is used for the prefix here. XPath expressions do not match
literally on the prefix, internally it is turned into a QName pair {
"http://dogs.com/some/schema", "name" }
and this pair is what is matched.   I don't know DOM 
well enough to describe how it would work for you.
There must be _some_ namespace binding context for
XPath to operate however...

Note that, in XSLT, the prefix is informational, since it 
is used by the XSLT processor to figure-out the appropriate QNames to look
for.  I hope this explains the statement above... that one can use the
prefix, however, this is 
different from making assumptions about it.

Best,

Clark

P.S.  There is an XSL list at mulberrytech.com which may 
be more appropriate for additional XSL questions.