• The developers of XSL were interested in creating a method of defining the formatting/presentation of XML documents
• The original XSL proposal was submitted to the W3C in August of 1997
• In early 1999 it became apparent that it would be better to think of XSL as two distinct components, XSL Transformations (XSLT) and XSL Formatting Objects (XSL-FO)
  • XSL-FO is similar in spirit to other types of stylesheets (including CSS and DSSSL)
  • XSLT is a language for selecting and processing the nodes in a document

• XSLT is a Data-Driven (as Opposed to Control-Driven) Language:
  • A program consists of a set of template rules, each of which describes how a particular element type should be processed
  • Rules can appear in any order
• Syntax:
  • Rules in an XSLT program are described using XML
  • All XSL tags are in the xsl namespace

• Side-Effects:
  • XSLT is free of side-effects
• Input:
  • Any XML document
• Output:
  • The most common output is HTML
  • XML
  • Text

When the conceptual (as opposed to actual) root element is encountered, we want to build the skeleton of the HTML document.

When a text (i.e., actual root) element is encountered, we want to insert a P element into the HTML skeleton, and insert the contents of the text element in the P.

The Complete Program

• Purpose:
  • The actual root element of all XSLT programs
• For Some Versions of IE:

  •         <xsl:stylesheet xmlns:xsl="http://www.w3.org/TR/WD-xsl"
                               result-ns="html">
            

• In General:

  •         <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
                               version="1.0">
    
            <xsl:output method="html" indent="yes"/>
    	

• Purpose:
  • Defines a template (or rule) for producing output
• Attributes:

  match

  The pattern that determines which nodes will be processed by this template.

• Purpose:
  • Indicates that the processor should search for and apply matching templates
• Attributes:

  select

  The pattern that determines which nodes will be processed. If this attribute is omitted, all nodes will be processed.

• Purpose:
  • Returns an XML node
• Attributes:

  select

  The pattern that determines which nodes will be processed. If this attribute is omitted, the current node will be returned. If more than one node is matched, only the first will be returned.

• Purpose:
  • Describe a sequence of "branches" in a document tree (i.e., a way of "finding" a node in the document tree.
• Operators:

  /	The child operator. It selects elements that are children of the specified node. For example, reference/year refers to the year element that is a child of the reference element.
  .	The current node operator. For example, ./year refers to the year element that is a child of the current element.
  @	The attribute operator. For example, train/@number refers to the number attribute of the train element.
  *	The wildcard operator. For example, timetable/* refers to all children of the timetable element.
  []	The index operator (1-based).

• Context Functions:
  • position() returns the index of the current node (1-based)
  • last() returns the index of the last node

• Purpose:
  • Allow elements to be selected
• Some Selection Criteria:
  • The existence of child nodes
  • The value of a node
  • The existence of an attribute
  • The value of an attribute
• Syntax:
  • [ operator pattern ]
  • where operator denotes a filter operator and pattern denotes a filter pattern

• Purpose:
  • Conditional processing
• Attributes:

  test	The pattern that determines the value of the test condition.

• Purpose:
  • Conditional processing
• Contains:
  • One or more xsl:when elements
  • At most one xsl:otherwise element
• Attributes:
  • Like xsl:if

• Continue Processing:
  • To allow recursive processing to continue in the absence of a match to an explicit rule there is a default rule that is equivalent to:

  • <xsl:template match="*|/">
      <xsl:apply-templates/>
    </xsl:template>
    	  

• Copy Through:
  • To copy text and attribute nodes there is a default rule that is equivalent to:

  • <xsl:template match="text()|@*">
      <xsl:value-of select="."/>
    </xsl:template>