Functions That Work with QNames

There are two XPath 2.0 functions designed to create expanded QName values xs:QName values:

  • fn:resolve-QName returns an xs:QName following the form given in the first argument. The prefix is resolved using the namespace nodes for a given element.

  • fn:expanded-QName returns an xs:QName with the namespace URI as given in the first argument and the local name as given in the second argument.

There is also a set of XPath 2.0 functions that are designed to work on xs:QName values:

  • fn:get-local-name-from-QName returns an xs:string value containing the local part of the xs:QName you pass to this function.

  • fn:get-namespace-uri-from-QName returns the namespace URI for the xs:QName value you pass.

  • fn:get- namespace-uri-for-prefix returns the namespace URI of the in-scope namespace for the given element, that is associated with the passed prefix.

  • fn:get- in-scope-prefixes returns a sequence of the prefixes of the in-scope namespaces for the given element.

We'll take a quick look at these functions here.

The fn:resolve-QName Function

This function creates an xs:QName value when you pass it a string, using the namespaces for a given element:

 
 fn:resolve-QName(  $qname  as xs:string,  $element  as element) as xs:QName 

The return value is an xs:QName value that depends on the form of the string you pass to iteither prefix:local-name or local-name . The prefix you pass to this function is resolved using the in-scope namespaces of the element you pass it.

Here's an example. Say that the element node in $element has one namespace node, which is bound to the prefix xdata . In that case, this expression returns an xs:QName with local name "data" that is not in any namespace:

 
 fn:resolve-QName("data", $element) 

On the other hand, the following expression returns an xs:QName value whose namespace URI is given by the URI of the namespace node matching the prefix xdata and whose local name is data :

 
 fn:resolve-QName("xdata:data", $element) 

The fn:expanded-QName Function

This function creates an xs:QName value when you pass it a namespace URI and a local name:

 
 fn:expanded-QName(  $URI  as xs:string,  $Local  as xs:string) as xs:QName 

The return value is an xs:QName that has the namespace URI given in $URI and the local name given in $Local . If $URI is an empty string, the return value has no namespace.

For example, this expression returns an xs:QName value with the namespace URI http://www.XPathCorp.com/actors and the local name carygrant :

 
 fn:expanded-QName("http://www.XPathCorp.com/actors", "carygrant") 

The fn:get-local-name-from-QName Function

The fn:get-local-name-from-QName function lets you retrieve the local name from an xs:QName value:

 
 fn:get-local-name-from-QName(  $srcval  as xs:QName?) as xs:string? 

The return value is an xs:string representing the local part of $srcval .

Here's an examplein this case, we're creating an xs:QName value with fn:expanded-QName("http://www.XPathCorp.com/actors", "carygrant") , and then extracting its local name. You can see how this works in ch11_07.xsl (Listing 11.7).

Listing 11.7 Using fn:get-local-name-from-QName ( ch11_07.xsl )
 <xsl:stylesheet version="2.0"     xmlns:xsl="http://www.w3.org/1999/XSL/Transform"     xmlns:xdt="http://www.w3.org/2003/05/xpath-datatypes"     xmlns:xs="http://www.w3.org/2001/XMLSchema">     <xsl:template match="/">  <xsl:value-of select="get-local-name-from-QName(   expanded-QName('http://www.XPathCorp.com/actors', 'carygrant'))"/>  </xsl:template> </xsl:stylesheet> 

And here is the result, showing that we have indeed been able to extract the local name of this xs:QName value:

 
 <?xml version="1.0" encoding="UTF-8"?> carygrant 

The fn:get-namespace-uri-from-QName Function

This function retrieves the namespace URI from an xs:QName value:

 
 fn:get-namespace-uri-from-QName(  $srcval  as xs:QName?) as xs:string? 

The return value is the namespace URI for $srcval as an xs:string .

You can see an example in ch11_08.xsl (Listing 11.8), where we're extracting the namespace URI from the xs:QName we created in the preceding example: fn:expanded-QName("http://www.XPathCorp.com/actors", "carygrant") . (Note that get-namespace-uri-from-QName was previously named get-namespace-from-QName , which is the way it's implemented in Saxon, so we'll call it that in this example's code.)

Listing 11.8 Using fn:get-namespace-from-QName ( ch11_08.xsl )
 <xsl:stylesheet version="2.0"     xmlns:xsl="http://www.w3.org/1999/XSL/Transform"     xmlns:xdt="http://www.w3.org/2003/05/xpath-datatypes"     xmlns:xs="http://www.w3.org/2001/XMLSchema">     <xsl:template match="/">  <xsl:value-of select="get-namespace-from-QName(   expanded-QName('http://www.XPathCorp.com/actors', 'carygrant'))"/>  </xsl:template> </xsl:stylesheet> 

And here is the result, showing the namespace URI we want:

 
 <?xml version="1.0" encoding="UTF-8"?> http://www.XPathCorp.com/actors 

The fn:get-namespace-uri-for-prefix Function

This function returns the namespace URI for a given prefix:

 
 fn:get-namespace-uri-for-prefix(  $element  as element,  $prefix  as xs:string) as xs:string? 

The return value is an xs:string that is the namespace URI of the in-scope namespace for $element that matches the namespace prefix in $prefix .

For example, if the element node in $element has an in-scope prefix xdata that corresponds to http://www.XPathCorp.com , the following would return "http://www.XPathCorp.com".

 
 fn:get-namespace-uri-for-prefix($element, "xdata") 

The fn:get-in-scope-prefixes Function

This function returns a sequence of the in-scope prefixes for an element. Here's how you use this function:

 
 fn:get-in-scope-namespaces(  $element  as element) as xs:string* 

To put this to work, we might add a new prefix, xdata , to our planetary data document like this:

 
 <?xml version="1.0"?>  <planets xmlns:xdata="http://www.XPathCorp.com">  <planet>         <name>Mercury</name>         <mass units="(Earth = 1)">.0553</mass>         <day units="days">58.65</day>         <radius units="miles">1516</radius>         <density units="(Earth = 1)">.983</density>         <distance units="million miles">43.4</distance>         <!--At perihelion-->     </planet>         .         .         . 

Now you can find the in-scope prefixes for the <planets> element as you see in ch11_09.xsl (Listing 11.9). (Saxon knows this function by its previous name, get-in-scope-namespaces , so we'll leave it like that for this example's code.)

Listing 11.9 Using fn:get-in-scope-namespaces ( ch11_09.xsl )
 <xsl:stylesheet version="2.0"     xmlns:xsl="http://www.w3.org/1999/XSL/Transform"     xmlns:xdt="http://www.w3.org/2003/05/xpath-datatypes"     xmlns:xs="http://www.w3.org/2001/XMLSchema">     <xsl:template match="/planets">  <xsl:value-of select="get-in-scope-namespaces(.)" separator=", "/>  </xsl:template> </xsl:stylesheet> 

Here are the results, showing the in-scope prefixes for the <planets> element, which are the xdata and the default xml prefixes:

 
 <?xml version="1.0" encoding="UTF-8"?> xdata, xml 


XPath. Navigating XML with XPath 1.0 and 2.0 Kick Start
XPath Kick Start: Navigating XML with XPath 1.0 and 2.0
ISBN: 0672324113
EAN: 2147483647
Year: 2002
Pages: 131

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