XSL

XSL (eXtensible Stylesheet Language)

1. Definition

XSL is the W3C family of standards for styling and transforming XML documents — because XML has no fixed tags, it needs a style language that can be told how to format any vocabulary.

The XSL family:

Part	Name	Purpose
XSLT	XSL Transformations	Transform XML → HTML, text, or another XML
XPath	XML Path Language	Address/select nodes inside an XML tree (used by XSLT)
XSL-FO	XSL Formatting Objects	Precise print/PDF page layout (now less used)

2. Why XSL?

XML separates data from presentation; XSL is the presentation layer.
One XML source → many outputs: HTML for a browser, WML for a phone, PDF for print, RSS for syndication.
Supports sorting, filtering, reordering, computed values — not just styling.

3. XSLT Working

 XML document + XSLT style sheet --> XSLT PROCESSOR --> result (HTML/XML/text)
      (input tree)   (rules/templates)   XPath selects   (output tree)

An XSLT style sheet is itself an XML document containing templates; each template matches a node (via XPath) and emits output.

<?xml version="1.0"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:template match="/">
    <html><body>
      <h2>Student List</h2>
      <table border="1">
        <xsl:for-each select="class/student">
          <tr>
            <td><xsl:value-of select="name"/></td>
            <td><xsl:value-of select="marks"/></td>
          </tr>
        </xsl:for-each>
      </table>
    </body></html>
  </xsl:template>
</xsl:stylesheet>

4. Important XSLT Elements

Element	Purpose
`<xsl:stylesheet>` / `<xsl:output method="html"/>`	Root / output format
`<xsl:template match="…">`	Rule applied to matched nodes
`<xsl:value-of select="…"/>`	Insert the text value of a node
`<xsl:for-each select="…">`	Loop over selected nodes
`<xsl:if test="…">` / `<xsl:choose>`	Conditional output
`<xsl:sort select="marks" order="descending"/>`	Sorting
`<xsl:apply-templates/>`	Continue processing children

5. XPath in One Minute

Expression	Selects
`/class`	Root element
`//student`	All student elements anywhere
`//student[marks > 80]`	Students with marks > 80 (predicate)
`//student/name/text()`	Text content
`@roll`	An attribute
`//book[3]`, `last()`, `position()`	Positional selection

6. XSL vs CSS

Aspect	CSS	XSL
Designed for	HTML (and simple XML)	Any XML
Can reorder/rename content?	No (display only)	Yes — full transformation
Can compute, sort, filter?	No	Yes
Output	Styled page	New document (HTML/XML/text/PDF via FO)
Syntax	Property declarations	XML templates + XPath

7. Exam Points

What is XSL? Explain the parts (XSLT, XPath, XSL-FO) — 7 marks.
Write an XSLT style sheet converting an XML student list to an HTML table — 10 marks (very frequent).
Compare XSL and CSS — 5 marks.
Basic XPath expressions — 5 marks.