XSLT Transformation Service

Transform input using the XML Stylesheet Language for Transformations (XSLT).

XSLT is a standard method to transform an XML structure from one document into a new document with a different structure.

The transformation expects the rule to be read from a file which is stored under the transform folder. To organize the various transformations one should use subfolders.

General transformation rule summary:

• The directive xsl:output defines how the output document should be structured.
• The directive xsl:template specifies matching attributes for the XML node to find.
• The xsl:template tag contains the rule which specifies what should be done.

The Rule uses XPath to gather the XML node information. For more information have a look at the XPath transformation (opens new window) .

Examples

Basic Example

A simple but complete XSLT transformation looks like in the following example, which was taken from here (opens new window).

input XML

<?xml version='1.0' encoding='UTF-8'?>
<root><node val='hello'/></root>

transform/helloworld.xsl

• xsl:output: transform incoming document into another XML-like document, without indentation.
• xsl:template: match="/" "any type of node", so the whole document.
• The xsl rule does select the node /root/node and extracts the value-of attribute val.

<?xml version='1.0' encoding='UTF-8'?>
<xsl:stylesheet version='2.0' xmlns:xsl='http://www.w3.org/1999/XSL/Transform'>
   <xsl:output method='xml' indent='no'/>
   <xsl:template match='/'>
      <reRoot><reNode><xsl:value-of select='/root/node/@val' /> world</reNode></reRoot>
   </xsl:template>
</xsl:stylesheet>

Output XML

<reRoot><reNode>hello world</reNode></reRoot>

Advanced Example

This example has a namespace defined, as you would find in real world applications, which has to be matched in the rule.

input XML

• The tag <PTZStatus> contains an attribute xmlns= which defines the namespace http://www.hikvision.com/ver20/XMLSchema.

<?xml version="1.0" encoding="UTF-8"?>
<PTZStatus version="2.0" xmlns="http://www.hikvision.com/ver20/XMLSchema">
    <AbsoluteHigh>
        <elevation>0</elevation>
        <azimuth date="Fri, 18 Dec 2009 9:38 am PST" >450</azimuth>
        <absoluteZoom>10</absoluteZoom>
    </AbsoluteHigh>
</PTZStatus>

transform/azimut.xsl

In the rule, the tag <xsl:stylesheet> has to have an attribute xmlns:xsl="http://www.w3.org/1999/XSL/Transform" and a second attribute xmlns:. This attribute has to be the same as the namespace for the input document. In the rule each step traversed along the path to the next tag has to be prepended with the xmlns namespace, here defined as h.

• xsl:output transform incoming document into another XML-like document, no indentation, without XML.
• xsl:template: match="/" whole document.
• Full path to node azimuth reading out date attribute.
• Add a linebreak by setting 
 as text.
• Search for node azimuth by prepending // and get the text.

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:h="http://www.hikvision.com/ver20/XMLSchema">
   <xsl:output method="xml" indent="no" encoding="UTF-8" omit-xml-declaration="yes"  />
   <xsl:template match="/">
      <xsl:value-of select="/h:PTZStatus/h:AbsoluteHigh/h:azimuth/@date" />
      <xsl:text>&#10;</xsl:text>
      <xsl:value-of select="//h:azimuth/text()" />
   </xsl:template>
</xsl:stylesheet>

Output Document

Fri, 18 Dec 2009 9:38 am PST
450

Usage as a Profile

The functionality of this TransformationService can be used in a Profile on an ItemChannelLink too. To do so, it can be configured in the .items file as follows:

String <itemName> { channel="<channelUID>"[profile="transform:XSLT", function="<xsltExpression>", sourceFormat="<valueFormat>"]}

The XSLT file (from within the transform folder) to be used has to be set in the function parameter. The parameter sourceFormat is optional and can be used to format the input value before the transformation, i.e. %.3f. If omitted the default is %s, so the input value will be put into the transformation without any format changes.

Please note: This profile is a one-way transformation, i.e. only values from a device towards the item are changed, the other direction is left untouched.

Further Reading

• Extended introduction and more examples (opens new window) at Wikipedia.
• A good introduction (opens new window) and tutorial (opens new window) at W3School.
• An informative tutorial (opens new window) of common mistakes.
• Online XSL transformer tools like this (opens new window) to check the syntax.

Caught a mistake or want to contribute to the documentation? Edit this page on GitHub (opens new window)