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XML Basics

Introduction to XMLXML SyntaxXML ElementsXML AttributesXML NamespacesXML CommentsXML CDATA SectionsXML White Space HandlingXML Encoding

XML Document Structure

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XML Transformation

XSLT IntroductionXSLT StylesheetsXSLT TemplatesXSLT ElementsXSLT FunctionsXSLT Sorting and GroupingXPath Expressions in XSLT

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XPath Expressions in XSLT

XPath expressions are a fundamental component of XSLT (eXtensible Stylesheet Language Transformations). They provide a powerful way to navigate and select nodes within an XML document, enabling precise and efficient XML transformations.

Understanding XPath in XSLT

XPath expressions in XSLT allow you to:

  • Select specific nodes or node-sets
  • Navigate through the XML document tree
  • Perform calculations and comparisons
  • Extract values from XML elements and attributes

These expressions are used within various XSLT elements, such as <xsl:value-of>, <xsl:for-each>, and <xsl:if>, to control the transformation process.

Basic XPath Syntax

XPath uses a path-like syntax to navigate through the XML document. Here are some common XPath expressions:

  • / - Selects from the root node
  • // - Selects nodes anywhere in the document
  • . - Selects the current node
  • .. - Selects the parent of the current node
  • @ - Selects attributes

Practical Examples

Let's look at some practical examples of using XPath expressions in XSLT:

Example 1: Selecting Elements

<xsl:template match="/">
  <xsl:for-each select="//book">
    <p><xsl:value-of select="title"/></p>
  </xsl:for-each>
</xsl:template>

This example selects all <book> elements in the document and outputs their titles.

Example 2: Using Predicates

<xsl:template match="/">
  <xsl:for-each select="//book[price > 20]">
    <p><xsl:value-of select="title"/> - $<xsl:value-of select="price"/></p>
  </xsl:for-each>
</xsl:template>

This example selects <book> elements with a price greater than 20 and outputs their titles and prices.

Advanced XPath Features

XPath in XSLT also supports more advanced features:

  • Functions (e.g., count(), sum(), concat())
  • Axes (e.g., ancestor::, descendant::, following-sibling::)
  • Wildcards (e.g., * for any element, @* for any attribute)

Best Practices

  • Use specific XPath expressions to improve performance
  • Avoid overly complex expressions that are hard to maintain
  • Consider using XPath variables for frequently used expressions
  • Test XPath expressions thoroughly with various XML inputs

Related Concepts

To deepen your understanding of XPath expressions in XSLT, explore these related topics:

By mastering XPath expressions in XSLT, you'll be able to create powerful and efficient XML transformations, enhancing your ability to process and manipulate XML data effectively.