XSL: Transformations and Style

Extensible Stylesheet Language (XSL)

XSL is a language for expressing stylesheets

• support for browsing, printing, and aural rendering
• formatting highly structured documents (XML)
• performing complex publishing tasks: tables of contents, indexes, reports,...
• addressing accessibility and internationalization issues
• written in XML

XSL Architecture

XSL Components

XSL is constituted of three main components:

• XSLT: a transformation language
• XPath: an expression language for addressing parts of XML documents
• FO: a vocabulary of formatting objects with their associated formatting properties

XSL uses XSLT which uses XPath

XSL Transformations

XSLT - Basic Principle

Patterns and Templates

• A style sheets describes transformation rules
• A transformation rule: a pattern + a template
• Pattern: a configuration in the source tree
• Template: a structure to be instantiated in the result tree
• When a pattern is matched in the source tree, the corresponding pattern is generated in the result tree

An Example: Transformation

<xsl:template match="Title">
   <H1>
      <xsl:apply-templates/>
   </H1>
</xsl:template>

Input : <Title>Introduction</Title>

Output : <H1>Introduction</H1>

An Example: Formatting

<xsl:stylesheet
     xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
     xmlns:fo="http://www.w3.org/1999/XSL/Format"
     result-ns="fo">
  <xsl:template match="/">
    <fo:page-sequence font-family="serif">
       <xsl:apply-templates/>
    </fo:page-sequence>
  </xsl:template>
  <xsl:template match="para">
    <fo:block font-size="10pt" space-before="12pt">
      <xsl:apply-templates/>
    </fo:block>
  </xsl:template>
</xsl:stylesheet>

XPath: XML Path Language

An elementary XPath expression contains

• an axis, which specifies the tree relationship: child, descendants, ancestors, siblings, attributes,...
• a node test, which specifies the node type
• predicates, to further refine the set of nodes selected

Example: all para children that have a type attribute with value warning

     child::para[attribute::type="warning"]

XSL Usage

• Format XML documents by generating FOs
• Generate HTML or XHTML pages from XML data/documents
• Transform XML documents into other XML documents
• Generate some textual representation of an XML document
• ...and more

XSL may be used server-side or client-side,
but is not intended to send FOs over the wire

Implementations

XSL software include:

• XSLT transformation engines: 4XSLT, IE5, iXSLT, LotusXSL, Transformiix, Resin, Sablotron, Saxon, Xalan, XML Parser (Oracle), XT
• FO formatters: FOP, FO2PDF, InDelv browser, Passive TeX, REXP
• XSL stylesheet editors
• Style sheets and transformation sheets

XSL and CSS

XSL is not intended to replace CSS, but provides functionality beyond that of CSS

XSL/CSS Common features:

• Formatting model
• Properties and values

History

XSL is inspired by both CSS and DSSSL (ISO/IEC 10179:1996)

• Sep 1997: "A Proposal for XSL" submitted to W3C by Inso, Microsoft, ArborText, U. of Edinburgh
• Jan 1998: The W3C Working Group for XSL is formed
• Feb 1998: The XSL list starts up
• Aug 1998: The first XSL working draft is published
• Apr 1999: The third XSL working draft is released. A separate document specifies the transformation language (XSLT)
• Jul 1999: A new working draft of XSLT is released. The expression language is specified in a separate working draft, XPath (with XML Linking WG)
• Aug 1999: XSLT, XPath enter Last Call
• Oct 1999: XSLT, XPath move to Proposed Recommendation status
• Nov 1999: XSLT, XPath become W3C Recommendations.
• Jan 2000: New XSL (FO) working draft published
• Mar 2000: XSL enters Last Call

Current Situation

• XPath 1.0 is a W3C Recommendation
• XSLT 1.0 is a W3C Recommendation
• XSL (FO) is in Last Call

What the Future Holds

Next step: move XSL 1.0 to W3C Recommendation status

New WG proposed to work on new versions of all 3 specifications: XSL, XSLT, XPath

• FOs: additional support of internationalized formatting objects, general regions
• XSLT, XPath: expanded extension mechanism, requirements from appendix G of XSLT version 1.0

XPath is used in XPointer and XLink, considered by XML Query WG

More information

W3C XSL page: http://www.w3.org/Style/XSL

XSL, XSLT, XPath specifications: http://www.w3.org/TR

Public mailing list: http://www.mulberrytech.com/xsl/xsl-list