S7 - IWP notes - XSL Languages

XSL Languages

It started with XSL and ended up with XSLT, XPath, and XSL-FO. XSL stands for  EXtensible  Stylesheet Language. The World Wide Web Consortium (W3C) started to develop XSL because there was a need for an XML-based Stylesheet Language.

CSS = Style Sheets for HTML

HTML uses predefined tags, and the meaning of each tag is well understood. The <table> tag in HTML defines a table - and a browser knows how to display it. Adding styles to HTML elements are simple. Telling a browser to display an element in a special font or color, is easy with CSS. 

XSL = Style Sheets for XML

XML does not use predefined tags (we can use any tag-names we like), and therefore the meaning of each tag is not well understood.

A <table> tag could mean an HTML table, a piece of furniture, or something else - and a browser does not know how to display it.

XSL describes how the XML document should be displayed!

XSL - More Than a Style Sheet Language

XSL consists of three parts:

• XSLT - a language for transforming XML documents
• XPath - a language for navigating in XML documents
• XSL-FO - a language for formatting XML documents

XSLT Introduction

XSLT is a language for transforming XML documents into XHTML documents or to other XML documents. XPath is a language for navigating in XML documents.

What is XSLT?

• XSLT stands for XSL Transformations
• XSLT is the most important part of XSL
• XSLT transforms an XML document into another XML document
• XSLT uses XPath to navigate in XML documents
• XSLT is a W3C Recommendation

XSLT = XSL Transformations

XSLT is used to transform an XML document into another XML document, or another type of document that is recognized by a browser, like HTML and XHTML. Normally XSLT does this by transforming each XML element into an (X)HTML element.

With XSLT you can add/remove elements and attributes to or from the output file. You can also rearrange and sort elements, perform tests and make decisions about which elements to hide and display, and a lot more. A common way to describe the transformation process is to say that XSLT transforms an XML source-tree into an XML result-tree.

How Does it Work?

In the transformation process, XSLT uses XPath to define parts of the source document that should match one or more predefined templates. When a match is found, XSLT will transform the matching part of the source document into the result document.

XSLT Browsers

All major browsers have support for XML and XSLT.

Correct Style Sheet Declaration

The root element that declares the document to be an XSL style sheet is <xsl:stylesheet> or <xsl:transform>.

Note: <xsl:stylesheet> and <xsl:transform> are completely synonymous and either can be used!

The correct way to declare an XSL style sheet according to the W3C XSLT Recommendation is:

<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

or:

<xsl:transform version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

To get access to the XSLT elements, attributes and features we must declare the XSLT namespace at the top of the document.

The xmlns:xsl="http://www.w3.org/1999/XSL/Transform" points to the official W3C XSLT namespace. If you use this namespace, you must also include the attribute version="1.0".

Start with a Raw XML Document

We want to transform the following XML document ("cdcatalog.xml") into XHTML:

<?xml version="1.0" encoding="ISO-8859-1"?>
<catalog>
  <cd>
    <title>Empire Burlesque</title>
    <artist>Bob Dylan</artist>
    <country>USA</country>
    <company>Columbia</company>
    <price>10.90</price>
    <year>1985</year>
  </cd>
</catalog>

Viewing XML Files in Firefox and Internet Explorer: Open the XML file (typically by clicking on a link) - The XML document will be displayed with color-coded root and child elements. A plus (+) or minus sign (-) to the left of the elements can be clicked to expand or collapse the element structure. To view the raw XML source (without the + and - signs), select "View Page Source" or "View Source" from the browser menu.

---

Create an XSL Style Sheet

Then you create an XSL Style Sheet ("cdcatalog.xsl") with a transformation template:

<?xml version="1.0" encoding="ISO-8859-1"?>

<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:template match="/">
  <html>
  <body>
  <h2>My CD Collection</h2>
  <table border="1">
    <tr bgcolor="#9acd32">
      <th>Title</th>
      <th>Artist</th>
    </tr>
    <xsl:for-each select="catalog/cd">
    <tr>
      <td><xsl:value-of select="title"/></td>
      <td><xsl:value-of select="artist"/></td>
    </tr>
    </xsl:for-each>
  </table>
  </body>
  </html>
</xsl:template>

</xsl:stylesheet>

Link the XSL Style Sheet to the XML Document

Add the XSL style sheet reference to your XML document ("cdcatalog.xml"):

<?xml version="1.0" encoding="ISO-8859-1"?>
<?xml-stylesheet type="text/xsl" href="cdcatalog.xsl"?>
<catalog>
  <cd>
    <title>Empire Burlesque</title>
    <artist>Bob Dylan</artist>
    <country>USA</country>
    <company>Columbia</company>
    <price>10.90</price>
    <year>1985</year>
  </cd>
</catalog>

If you have an XSLT compliant browser it will nicely transform your XML into XHTML.

XSLT <xsl:template> Element

An XSL style sheet consists of one or more set of rules that are called templates. A template contains rules to apply when a specified node is matched.

The <xsl:template> Element

The <xsl:template> element is used to build templates.

The match attribute is used to associate a template with an XML element. The match attribute can also be used to define a template for the entire XML document. The value of the match attribute is an XPath expression (i.e. match="/" defines the whole document).

Example

<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:template match="/">
  <html>
  <body>
  <h2>My CD Collection</h2>
  <table border="1">
    <tr bgcolor="#9acd32">
      <th>Title</th>
      <th>Artist</th>
    </tr>
    <tr>
      <td>.</td>
      <td>.</td>
    </tr>
  </table>
  </body>
  </html>
</xsl:template>

</xsl:stylesheet>

Example Explained

Since an XSL style sheet is an XML document, it always begins with the XML declaration: <?xml version="1.0" encoding="ISO-8859-1"?>.

The next element, <xsl:stylesheet>, defines that this document is an XSLT style sheet document (along with the version number and XSLT namespace attributes).

The <xsl:template> element defines a template. The match="/" attribute associates the template with the root of the XML source document.

The content inside the <xsl:template> element defines some HTML to write to the output.

The last two lines define the end of the template and the end of the style sheet.

The result from this example was a little disappointing, because no data was copied from the XML document to the output. In the next chapter you will learn how to use the <xsl:value-of> element to select values from the XML elements.

XSLT <xsl:value-of> Element

The <xsl:value-of> element can be used to extract the value of an XML element and add it to the output stream of the transformation:

XSLT <xsl:for-each> Element

The XSL <xsl:for-each> element can be used to select every XML element of a specified node-set:

Filtering the Output

We can also filter the output from the XML file by adding a criterion to the select attribute in the <xsl:for-each> element.    <xsl:for-each select="catalog/cd[artist='Bob Dylan']">

Legal filter operators are:

• =  (equal)
• != (not equal)
• &lt; less than
• &gt; greater than

Take a look at the adjusted XSL style sheet:

<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:template match="/">
  <html>
  <body>
  <h2>My CD Collection</h2>
  <table border="1">
    <tr bgcolor="#9acd32">
      <th>Title</th>
      <th>Artist</th>
    </tr>
    <xsl:for-each select="catalog/cd[artist='Bob Dylan']">
    <tr>
      <td><xsl:value-of select="title"/></td>
      <td><xsl:value-of select="artist"/></td>
    </tr>
    </xsl:for-each>
  </table>
  </body>   </html> </xsl:template> </xsl:stylesheet>