XSL(T) Languages - The Coding College

Welcome to The Coding College! In this article, we’ll explore XSL(T) Languages, their components, and how they work together to transform XML data into meaningful outputs like HTML, text, or other XML formats. If you’re working with XML data and need to style, transform, or structure it, understanding XSL(T) is essential.

What Is XSL?

XSL (Extensible Stylesheet Language) is a family of languages used to transform and render XML documents. These languages define the rules for presenting and restructuring XML data, and they consist of three main components:

XSLT (XSL Transformations):
Transforms XML into other formats like HTML, plain text, or different XML structures.
XPath (XML Path Language):
A query language used within XSLT to navigate and select parts of an XML document.
XSL-FO (XSL Formatting Objects):
Defines the styling and layout for presenting XML data, primarily for printing or rendering to PDF.

XSLT: The Core of XSL

XSLT is the most widely used component of XSL. It allows XML data to be transformed into different outputs through templates and rules defined in an XSLT stylesheet.

Key Features of XSLT:

Transform XML into web pages (HTML), plain text files, or other XML formats.
Use XPath to locate and manipulate XML nodes.
Support for conditional logic, looping, and variable assignments.

Example: Transform XML to HTML

XML Input:

<bookstore>
  <book>
    <title>XML Basics</title>
    <author>John Doe</author>
    <price>29.99</price>
  </book>
  <book>
    <title>Advanced XSLT</title>
    <author>Jane Smith</author>
    <price>39.99</price>
  </book>
</bookstore>

XSLT Stylesheet:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
  <xsl:template match="/">
    <html>
      <body>
        <h1>Bookstore</h1>
        <table border="1">
          <tr>
            <th>Title</th>
            <th>Author</th>
            <th>Price</th>
          </tr>
          <xsl:for-each select="bookstore/book">
            <tr>
              <td><xsl:value-of select="title" /></td>
              <td><xsl:value-of select="author" /></td>
              <td><xsl:value-of select="price" /></td>
            </tr>
          </xsl:for-each>
        </table>
      </body>
    </html>
  </xsl:template>
</xsl:stylesheet>

Output HTML:

<html>
  <body>
    <h1>Bookstore</h1>
    <table border="1">
      <tr>
        <th>Title</th>
        <th>Author</th>
        <th>Price</th>
      </tr>
      <tr>
        <td>XML Basics</td>
        <td>John Doe</td>
        <td>29.99</td>
      </tr>
      <tr>
        <td>Advanced XSLT</td>
        <td>Jane Smith</td>
        <td>39.99</td>
      </tr>
    </table>
  </body>
</html>

XPath: The Query Engine

XPath is a companion technology to XSLT that is used to navigate and query XML documents.

Key Features of XPath:

Navigate through XML elements and attributes.
Select nodes using paths or expressions.
Perform comparisons, calculations, and logical operations.

Common XPath Syntax:

Expression	Description
`/`	Selects the root node.
`//`	Selects nodes in the document from anywhere.
`@attribute`	Selects an attribute of a node.
`[condition]`	Filters nodes by a condition.

Example: Selecting Nodes with XPath

/bookstore/book/title

Result: Selects all <title> elements in <book> elements within <bookstore>.

XSL-FO: Styling and Formatting

XSL-FO (Formatting Objects) is used to define how XML data is styled and laid out for presentation. While less commonly used than XSLT, XSL-FO is powerful for creating printed documents like PDFs.

Key Features of XSL-FO:

Define layouts, such as page size, margins, headers, and footers.
Style text with fonts, colors, and alignment.
Render content for high-quality print output.

Example: Basic XSL-FO Document

<fo:root xmlns:fo="http://www.w3.org/1999/XSL/Format">
  <fo:layout-master-set>
    <fo:simple-page-master master-name="simple" page-height="11in" page-width="8.5in" margin="1in">
      <fo:region-body />
    </fo:simple-page-master>
  </fo:layout-master-set>
  <fo:page-sequence master-reference="simple">
    <fo:flow flow-name="xsl-region-body">
      <fo:block>Hello, XSL-FO!</fo:block>
    </fo:flow>
  </fo:page-sequence>
</fo:root>

This generates a document with “Hello, XSL-FO!” styled for print output.

Comparing XSLT, XPath, and XSL-FO

Component	Purpose	Example Use Case
XSLT	Transform XML into other formats.	Generate HTML pages from XML data.
XPath	Navigate and query XML data.	Extract a list of node values from XML.
XSL-FO	Define the layout and style of documents.	Create PDF reports from XML.

When to Use XSLT, XPath, and XSL-FO

XSLT: Use for data transformation, like converting XML to HTML.
XPath: Use within XSLT or standalone to extract or filter data from XML.
XSL-FO: Use for high-quality print layouts or generating PDFs.

Conclusion

The XSL family of languages provides a comprehensive solution for working with XML data. Whether you need to transform XML into web content (XSLT), query XML documents (XPath), or style XML for print (XSL-FO), these technologies give you the tools to get the job done.