C XSLT Primer

This appendix describes introductory information about the W3C XSL and XSLT Recommendation.

This appendix contains these topics:

Overview of XSL
XSL Transformation (XSLT)
XML Path Language (Xpath)
CSS Versus XSL
XSL Style Sheet Example, PurchaseOrder.xsl

Overview of XSL

XML documents have structure but no format. The Extensible Stylesheet Language (XSL) adds formatting to XML documents. It provides a way to display XML semantics and can map XML elements into other formatting languages such as HTML.

See Also:

W3C XSL Transformation Recommendation Version 1.0

This specification defines the syntax and semantics of XSLT, which is a language for transforming XML documents into other XML documents.

XSLT is designed for use as part of XSL, which is a style sheet language for XML. In addition to XSLT, XSL includes an XML vocabulary for specifying formatting. XSL specifies the styling of an XML document by using XSLT to describe how the document is transformed into another XML document that uses the formatting vocabulary.

XSLT is also designed to be used independently of XSL. However, XSLT is not intended as a completely general-purpose XML transformation language. Rather it is designed primarily for the kinds of transformations that are needed when XSLT is used as part of XSL.

See Also:

http://www.w3.org/TR/xslt

This specification defines the syntax and semantics of the XSLT language. A transformation in the XSLT language is expressed as a well-formed XML document conforming to the Namespaces in XML Recommendation, which may include both elements that are defined by XSLT and elements that are not defined by XSLT.

XSLT-defined elements are distinguished by belonging to a specific XML namespace (see [2.1 XSLT Namespace]), which is referred to in this specification as the XSLT namespace. Thus this specification is a definition of the syntax and semantics of the XSLT namespace.

A transformation expressed in XSLT describes rules for transforming a source tree into a result tree. The transformation is achieved by associating patterns with templates. A pattern is matched against elements in the source tree. A template is instantiated to create part of the result tree. The result tree is separate from the source tree. The structure of the result tree can be completely different from the structure of the source tree. In constructing the result tree, elements from the source tree can be filtered and reordered, and arbitrary structure can be added.

A transformation expressed in XSLT is called a style sheet. This is because, when XSLT is transforming into the XSL formatting vocabulary, the transformation functions as a style sheet.

This appendix does not specify how an XSLT style sheet is associated with an XML document. It is recommended that XSLT processors support the mechanism described in. When this or any other mechanism yields a sequence of more than one XSLT style sheet to be applied simultaneously to a XML document, then the effect should be the same as applying a single style sheet that imports each member of the sequence in order.

A style sheet contains a set of template rules. A template rule has two parts: a pattern which is matched against nodes in the source tree and a template which can be instantiated to form part of the result tree. This allows a style sheet to be applicable to a wide class of documents that have similar source tree structures.

The W3C is developing the XSL specification as part of its Style Sheets Activity. XSL has document manipulation capabilities beyond styling. It is a style sheet language for XML.

The July 1999 W3C XSL specification, was split into two separate documents:

XSL syntax and semantics
How to use XSL to apply style sheets to transform one document into another

The formatting objects used in XSL are based on prior work on Cascading Style Sheets (CSS) and the Document Style Semantics & Specification Language (DSSSL). CSS use a simple mechanism for adding style (fonts, colors, spacing, and so on) to Web documents. XSL is designed to be easier to use than DSSSL.

Capabilities provided by XSL as defined in the proposal enable the following functionality:

Formatting of source elements based on ancestry and descendency, position, and uniqueness
The creation of formatting constructs including generated text and graphics
The definition of reusable formatting macros
Writing-direction independent style sheets
An extensible set of formatting objects.

See Also:
http://www.w3.org/Style/XSL/

Namespaces in XML

A namespace is a unique identifier or name. This is needed because XML documents can be authored separately with different Document Type Definitions (DTDs) or XML schemas. Namespaces prevent conflicts in markup tags by identifying which DTD or XML schema a tag comes from. Namespaces link an XML element to a specific DTD or XML schema.

Before you can use a namespace marker such as rml:, xhtml:, or xsl:, you must identify it using the namespace indicator, xmlns as shown in the next paragraph.

See Also:

http://www.w3.org/TR/REC-xml-names/

XSL Style Sheet Architecture

The XSLT style sheets must include the following syntax:

Start tag stating the style sheet, such as <xsl:stylesheet2>
Namespace indicator, such as xmlns:xsl="http//www.w3.org/TR/WD-xsl" for an XSL namespace indicator and xmlns:fo="http//www.w3.org/TR/WD-xsl/FO" for a formatting object namespace indicator
Template rules including font families and weight, colors, and breaks. The templates have instructions that control the element and element values
End of style sheet declaration, </xsl:stylesheet2>

XSL Transformation (XSLT)

XSLT is designed to be used as part of XSL. In addition to XSLT, XSL includes an XML vocabulary for specifying formatting. XSL specifies the styling of an XML document by using XSLT to describe how the document is transformed into another XML document that uses the formatting vocabulary.

Meanwhile the second part is concerned with the XSL formatting objects, their attributes, and how they can be combined.

XML Path Language (Xpath)

A separate, related specification is published as the XML Path Language (XPath) Version 1.0. XPath is a language for addressing parts of an XML document, essential for cases where you want to specify exactly which parts of a document are to be transformed by XSL. For example, XPath lets you select all paragraphs belonging to the chapter element, or select the elements called special notes. XPath is designed to be used by both XSLT and XPointer. XPath is the result of an effort to provide a common syntax and semantics for functionality shared between XSL transformations and XPointer.

CSS Versus XSL

W3C is working to ensure that interoperable implementations of the formatting model is available.

Cascading Style Sheets (CSS) can be used to style HTML documents. CSS were developed by the W3C Style Working Group. CSS2 is a style sheet language that allows authors and users to attach styles (for example, fonts, spacing, or aural cues) to structured documents, such as HTML documents and XML applications.

By separating the presentation style of documents from the content of documents, CSS2 simplifies Web authoring and website maintenance.

XSL, on the other hand, is able to transform documents. For example, XSL can be used to transform XML data into HTML/CSS documents on the Web server. This way, the two languages complement each other and can be used together. Both languages can be used to style XML documents. CSS and XSL will use the same underlying formatting model and designers will therefore have access to the same formatting features in both languages.

The model used by XSL for rendering documents on the screen builds on years of work on a complex ISO-standard style language called DSSSL. Aimed mainly at complex documentation projects, XSL also has many uses in automatic generation of tables of contents, indexes, reports, and other more complex publishing tasks.

XSL Style Sheet Example, PurchaseOrder.xsl

The following example, PurchaseOrder.xsl, is an example of an XSLT style sheet. The example style sheet is used in examples in Chapter 3, "Using Oracle XML DB".

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0"  
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
                xmlns:xdb="http://xmlns.oracle.com/xdb" 
                xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <xsl:template match="/">
    <html>
      <head/>
      <body bgcolor="#003333" text="#FFFFCC" link="#FFCC00"             
            vlink="#66CC99" alink="#669999">
        <FONT FACE="Arial, Helvetica, sans-serif">
          <xsl:for-each select="PurchaseOrder"/>
          <xsl:for-each select="PurchaseOrder">
            <center>
              <span style="font-family:Arial; font-weight:bold">
                <FONT COLOR="#FF0000">
                  <B>Purchase Order </B>
                </FONT>
              </span>
            </center>
            <br/>
            <center>
              <xsl:for-each select="Reference">
                <span style="font-family:Arial; font-weight:bold">
                  <xsl:apply-templates/>
                </span>
              </xsl:for-each>
            </center>
          </xsl:for-each>
          <P>
            <xsl:for-each select="PurchaseOrder">
              <br/>
            </xsl:for-each>
            <P/>
            <P>
              <xsl:for-each select="PurchaseOrder">
                <br/>
              </xsl:for-each>
            </P>
          </P>
          <xsl:for-each select="PurchaseOrder"/>
          <xsl:for-each select="PurchaseOrder">
            <table border="0" width="100%" BGCOLOR="#000000">
              <tbody>
                <tr>
                  <td WIDTH="296">
                    <P>
                      <B>
                        <FONT SIZE="+1" COLOR="#FF0000" 
                         FACE="Arial, Helvetica, sans-serif">Internal
                        </FONT>
                      </B>
                    </P>
                    <table border="0" width="98%" BGCOLOR="#000099">
                      <tbody>
                        <tr>
                          <td WIDTH="49%">
                            <B>
                              <FONT COLOR="#FFFF00">Actions</FONT>
                            </B>
                          </td>
                          <td WIDTH="51%">
                            <xsl:for-each select="Actions">
                              <xsl:for-each select="Action">
                                <table border="1" WIDTH="143">
                                  <xsl:if test="position()=1">
                                    <thead>
                                      <tr>
                                        <td HEIGHT="21">
                                          <FONT  
                                           COLOR="#FFFF00">User</FONT>
                                        </td>
                                        <td HEIGHT="21">
                                          <FONT
                                           COLOR="#FFFF00">Date</FONT>
                                        </td>
                                      </tr>
                                    </thead>
                                  </xsl:if>
                                  <tbody>
                                    <tr>
                                      <td>
                                        <xsl:for-each select="User">
                                          <xsl:apply-templates/>
                                        </xsl:for-each>
                                      </td>
                                      <td>
                                        <xsl:for-each select="Date">
                                          <xsl:apply-templates/>
                                        </xsl:for-each>
                                      </td>
                                    </tr>
                                  </tbody>
                                </table>
                              </xsl:for-each>
                            </xsl:for-each>
                          </td>
                        </tr>
                        <tr>
                          <td WIDTH="49%">
                            <B>
                              <FONT COLOR="#FFFF00">Requestor</FONT>
                            </B>
                          </td>
                          <td WIDTH="51%">
                            <xsl:for-each select="Requestor">
                              <xsl:apply-templates/>
                            </xsl:for-each>
                          </td>
                        </tr>
                        <tr>
                          <td WIDTH="49%">
                            <B>
                              <FONT COLOR="#FFFF00">User</FONT>
                            </B>
                          </td>
                          <td WIDTH="51%">
                            <xsl:for-each select="User">
                              <xsl:apply-templates/>
                            </xsl:for-each>
                          </td>
                        </tr>
                        <tr>
                          <td WIDTH="49%">
                            <B>
                              <FONT COLOR="#FFFF00">Cost Center</FONT>
                            </B>
                          </td>
                          <td WIDTH="51%">
                            <xsl:for-each select="CostCenter">
                              <xsl:apply-templates/>
                            </xsl:for-each>
                          </td>
                        </tr>
                      </tbody>
                    </table>
                  </td>
                  <td width="93"/>
                  <td valign="top" WIDTH="340">
                    <B>
                      <FONT COLOR="#FF0000">
                        <FONT SIZE="+1">Ship To</FONT>
                      </FONT>
                    </B>
                    <xsl:for-each select="ShippingInstructions">
                      <xsl:if test="position()=1"/>
                    </xsl:for-each>
                    <xsl:for-each select="ShippingInstructions">
                      <xsl:if test="position()=1">
                        <table border="0" BGCOLOR="#999900">
                          <tbody>
                            <tr>
                              <td WIDTH="126" HEIGHT="24">
                                <B>Name</B>
                              </td>
                              <xsl:for-each
                                   select="../ShippingInstructions">
                                <td WIDTH="218" HEIGHT="24">
                                  <xsl:for-each select="name">
                                    <xsl:apply-templates/>
                                  </xsl:for-each>
                                </td>
                              </xsl:for-each>
                            </tr>
                            <tr>
                              <td WIDTH="126" HEIGHT="34">
                                <B>Address</B>
                              </td>
                              <xsl:for-each 
                                   select="../ShippingInstructions">
                                <td WIDTH="218" HEIGHT="34">
                                  <xsl:for-each select="address">
                                    <span style="white-space:pre">
                                      <xsl:apply-templates/>
                                    </span>
                                  </xsl:for-each>
                                </td>
                              </xsl:for-each>
                            </tr>
                            <tr>
                              <td WIDTH="126" HEIGHT="32">
                                <B>Telephone</B>
                              </td>
                              <xsl:for-each  
                                   select="../ShippingInstructions">
                                <td WIDTH="218" HEIGHT="32">
                                  <xsl:for-each select="telephone">
                                    <xsl:apply-templates/>
                                  </xsl:for-each>
                                </td>
                              </xsl:for-each>
                            </tr>
                          </tbody>
                        </table>
                      </xsl:if>
                    </xsl:for-each>
                  </td>
                </tr>
              </tbody>
            </table>
            <br/>
            <B>
              <FONT COLOR="#FF0000" SIZE="+1">Items:</FONT>
            </B>
            <br/>
            <br/>
            <table border="0">
              <xsl:for-each select="LineItems">
                <xsl:for-each select="LineItem">
                  <xsl:if test="position()=1">
                    <thead>
                      <tr bgcolor="#C0C0C0">
                        <td>
                          <FONT COLOR="#FF0000">
                            <B>ItemNumber</B>
                          </FONT>
                        </td>
                        <td>
                          <FONT COLOR="#FF0000">
                            <B>Description</B>
                          </FONT>
                        </td>
                        <td>
                          <FONT COLOR="#FF0000">
                            <B>PartId</B>
                          </FONT>
                        </td>
                        <td>
                          <FONT COLOR="#FF0000">
                            <B>Quantity</B>
                          </FONT>
                        </td>
                        <td>
                          <FONT COLOR="#FF0000">
                            <B>Unit Price</B>
                          </FONT>
                        </td>
                        <td>
                          <FONT COLOR="#FF0000">
                            <B>Total Price</B>
                          </FONT>
                        </td>
                      </tr>
                    </thead>
                  </xsl:if>
                  <tbody>
                    <tr bgcolor="#DADADA">
                      <td>
                        <FONT COLOR="#000000">
                          <xsl:for-each select="@ItemNumber">
                            <xsl:value-of select="."/>
                          </xsl:for-each>
                        </FONT>
                      </td>
                      <td>
                        <FONT COLOR="#000000">
                          <xsl:for-each select="Description">
                            <xsl:apply-templates/>
                          </xsl:for-each>
                        </FONT>
                      </td>
                      <td>
                        <FONT COLOR="#000000">
                          <xsl:for-each select="Part">
                            <xsl:for-each select="@Id">
                              <xsl:value-of select="."/>
                            </xsl:for-each>
                          </xsl:for-each>
                        </FONT>
                      </td>
                      <td>
                        <FONT COLOR="#000000">
                          <xsl:for-each select="Part">
                            <xsl:for-each select="@Quantity">
                              <xsl:value-of select="."/>
                            </xsl:for-each>
                          </xsl:for-each>
                        </FONT>
                      </td>
                      <td>
                        <FONT COLOR="#000000">
                          <xsl:for-each select="Part">
                            <xsl:for-each select="@UnitPrice">
                              <xsl:value-of select="."/>
                            </xsl:for-each>
                          </xsl:for-each>
                        </FONT>
                      </td>
                      <td>
                        <FONT FACE="Arial, Helvetica, sans-serif" 
                              COLOR="#000000">
                          <xsl:for-each select="Part">
                            <xsl:value-of select="@Quantity*@UnitPrice"/>
                          </xsl:for-each>
                        </FONT>
                      </td>
                    </tr>
                  </tbody>
                </xsl:for-each>
              </xsl:for-each>
            </table>
          </xsl:for-each>
        </FONT>
      </body>
    </html>
  </xsl:template>
</xsl:stylesheet>