Resolving XML QNames
Alexandre Alves's Blog |
November 11, 2005 5:49 PM
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Comments (0)
The XML Namespace specification defines the concept of a qualified name as a name
consisting of a local part and namespace URI.
A qualified name, or QName, is specified in terms of a
prefix and a local part (e.g. <foo:bar xmlns:foo='urn:foo'>),
where the prefix (foo) is resolved to a namespace URI ('urn:foo').
This process of resolving the prefix results in what is commonly known as the
expanded name.
The rules for resolving a prefix are mostly uniform in the
context of different XML processors, with the exception of how default
namespaces (e.g. xmlns='urn:foo') are dealt with.
Specifically:
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XML elements: if the QName does not have a prefix, then the
in-scope default namespace must be used.
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XML
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Resolved
namespace for element 'foo'
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<foo xmlns='urn:foo'/>
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'urn:foo'
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-
XML attributes: if the QName does not have a prefix, then the
namespace URI is NULL, that is, the default namespace is not used.
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XML
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Resolved
namespace for attribute 'a'
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<foo xmlns='urn:foo'a='attr1'/>
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NULL
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<foo xmlns:ns1='urn:foo' ns1:a='attr1' />
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'urn:foo'
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Attribute value of W3C Schema primitive type QName: if the QName
does not have a prefix, then the in-scope default namespace must be used.
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XML
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Resolved
namespace of attribute value of attribute 'a'
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<foo xmlns='urn:foo' a='myname'/>
where
<xsd:attribute name='a' type='xsd:QName'/>
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'urn:foo'
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XSLT (1.0) variable or parameter: if the QName does not have a
prefix, then the namespace URI is NULL, that is, the default namespace is not
used.
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XSLT
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Resolved
namespace for variable
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<xsl:variable name='varA' xmlns='urn:foo' />
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NULL
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<xsl:variable name='ns1:varA' xmlns='urn:foo'
xmlns:ns1='urn:bar' />
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'urn:bar'
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XPath 1.0 node tests: if the QName does not have a prefix, then
the namespace URI is NULL, that is, the default namespace is not used.
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XPATH
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Resolved
namespace for Node Test 'b'
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<a xmlns:ns1='urn:foo' xmlns='urn:foo'>
<b/>
</a>
/ns1:a/b
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NULL
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/ns1:a/ns1:b
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'urn:foo'
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XPath 2.0 node (name) tests: if the QName does not have a prefix,
then the in-scope default namespace must be used.
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XPATH
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Resolved
namespace for Node Test 'b'
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<a xmlns:ns1='urn:foo' xmlns='urn:foo'>
<b/>
</a>
/ns1:a/b
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'urn:foo'
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