XSL an introduction

XSL an introduction XSLT - An introduction

Ad Emmen Genias Benelux James Stewartstraat 24 NL-1325 JN Almere The Netherlands emmen@genias.nl http://www.genias.nl/

May 2002, Almere

Why XSLT

XML separates contents from formatting
An XML-tag like <b> does not mean anything by itself
For instance Bold, Big, Brown, Bubble
You need a formatting instruction to tell how it should be formatted
That is where stylesheets come in

XML Stylesheet languages: CSS and XSL

Cascading Style Sheets (CSS)

Same as for HTML
Tell how each element should be displayed
Useful for computer displays

Extensible Stylesheet Language (XSL)

More powerful
Also for printing and other display units
Detailed control over lay-out
Elements can be rearranged - transformed - before display

XSL, XSLT and XSL-FO

XSL consists of two separate languages plus a supporting standard
XSLT- transformation language
XSL-FO - formatting language
You also need XPath: way of addressing elements
XSLT can be used without XSL-FO: powerful in itself

What is XSLT

With XSLT you can transform one or more XML documents into a new one
Transformation process guided by an XSLT-Stylesheet
What is so special about that?
Well, remember also XHTML and WML are XML-documents
With XSLT you can create web sites and WAP sites

And that is not all..

Another important aspect of XML is its use for data-exchange and access
Merging machine data from site A with rankings from site B
Exchanging information through messages (SOAP)
Use XSLT to access the data and "web services" and produce a new XML document
The original data has to be available in XML
.. or a format that can be converted to XML like "raw" HTML with Tidy

An XML document

<?xml version="1.0" ?>
<ors:list-of-systems  
     xmlns:ors="http://www.hoise.com/ors/0.1"
     xmlns:vmp="http://www.hoise.com/vmp/manual/0.1" 
     id="gone">


<ors:system>
 <ors:name>Alex AVX 2</ors:name>
 <ors:year-of-introduction>1992</ors:year-of-introduction>  
 <ors:year-of-exit>1997</ors:year-of-exit>
 <ors:machine-type><ors:general>RISC-based distributed-memory multi-processor.</ors:general></ors:machine-type>
 <ors:peak-performance unit="gflops">3.84</ors:peak-performance>
 <ors:remarks>System is obsolete, there is no new system planned. </ors:remarks>
</ors:system>


<ors:system>
 <ors:name>Alliant FX/2800</ors:name>
 <ors:year-of-introduction>1989</ors:year-of-introduction>  
 <ors:year-of-exit>1992</ors:year-of-exit>
 <ors:machine-type><ors:general>Shared-memory vector-parallel, max. 28 processors.</ors:general></ors:machine-type>
 <ors:peak-performance unit="mflops">1120</ors:peak-performance>
 <ors:remarks>Manufacturer out of business.
 </ors:remarks>
</ors:system>


<ors:system>
 <ors:name>AxilSCC</ors:name>
 <ors:year-of-introduction>1996</ors:year-of-introduction>  
 <ors:year-of-exit>1997</ors:year-of-exit>
 <ors:machine-type><ors:general>RISC-based distributed-memory system, max. 512 processors.</ors:general></ors:machine-type>
 <ors:peak-performance unit="gflops">76.8</ors:peak-performance>
 <ors:remarks>System is not marketed anymore by Axil.
 </ors:remarks>
</ors:system>


<ors:system>
 <ors:name>BBN TC2000</ors:name>
 <ors:year-of-introduction>---</ors:year-of-introduction>  
 <ors:year-of-exit>1990</ors:year-of-exit>
 <ors:machine-type><ors:general> Virtual shared-memory parallel, max. 512 processors.</ors:general></ors:machine-type>
 <ors:peak-performance unit="gflops">1</ors:peak-performance>
 <ors:remarks>Manufacturer has discontinued marketing parallel computer systems.
 </ors:remarks>
</ors:system>

</ors:list-of-systems>

A basic XSLT Stylesheet copying the input document to the output

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet 
     xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
     version="1.0">


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

<xsl:template match="*|@*">
  <xsl:copy>
    <xsl:apply-templates select="@*"/>
    <xsl:apply-templates select="node()"/>
  </xsl:copy>
</xsl:template>

</xsl:stylesheet>

Stylesheets are XML documents
Document element: 'stylesheet' or 'transform'
Important is the name-space binding url
A stylesheet consists of templates and some other top level elements
Optional: DTD

Tree structure

XML documents have a tree-like structure
There is only one starting element: the root
The root contains one document-element
Attributes are considered "leaves" of the element to which they belong
An XSLT processor takes an input tree and converts it to an output tree

A basic XSLT Stylesheet doing something

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

  <xsl:template match="system">
    <h3><xsl:value-of select="name"/></h3>
  </xsl:template>

</xsl:stylesheet>

xsl:template works recursively for all "system"-elements
In the output it will put the contents of the "name"-element, surrounded by HTML-type heading-3 tags
Will not work with our example file:
Include namespace "ors"
Provide a starting element for the XSLT-processor

Creating a complete HTML document

<?xml version="1.0"?>
<xsl:stylesheet 
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
      xmlns:ors="http://www.hoise.com/ors/0.1"> 

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

<xsl:template match="ors:list-of-systems">
<html>
 <head>
 </head>
 <body>
  <xsl:apply-templates />
 </body>
</html>
</xsl:template>

  <xsl:template match="ors:system">
    <h3><xsl:value-of select="ors:name"/></h3>
<p><b><xsl:text>Year-of-Introduction: </xsl:text></b><xsl:value-of select="ors:year-of-introduction"/></p>
  </xsl:template>

</xsl:stylesheet>

The "ors"-namespace has been added
The document-element "ors:list-of-systems" now results in a complete html file
"xsl:text" is used to insert text - especially useful for leading and trailing spaces

Matching elements

Templates work when they find a match
You match elements by their name
Position is relative to the postion of the current element
"/" matches root
"," matches contents of current element
"name" matches children with name "name"
"name/othername" matches children with name "othername" with parent "name"
"name/*" matches all elements with parent "name"
And more. In general: should be an XPath expression

Matching examples

<xsl:template match="ors:system"/> matches "ors:system"
<xsl:template match="system"/> matches "system" not "ors:system"
<xsl:template match="ors:machine-type/ors:general"/> matches "ors:general" elements with parent "ors:machine-type"
<xsl:template match="ors:general"/> matches "ors:general" elements

Narrowing selections

name["." = "this"] selects only elements with name "name" and contents "this"]
system[year-of-exit > "1992"] selects the element 'system' whith a child-elem=ent year-of-exit' with content '1992'

Example


<?xml version="1.0"?>
<xsl:stylesheet 
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
      xmlns:ors="http://www.hoise.com/ors/0.1"> 

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

<xsl:template match="ors:list-of-systems">
<html>
 <head>
 </head>
 <body>
  <xsl:apply-templates />
 </body>
</html>
</xsl:template>

<xsl:template match="ors:system">
 <h3><xsl:value-of select="ors:name"/></h3>
 <p><b><xsl:text>Year-of-Introduction: </xsl:text></b>
 <xsl:apply-templates select="ors:year-of-introduction"/></p>
</xsl:template>


<xsl:template match="ors:year-of-introduction[ . >= '1992']">  
 <font color="red"><xsl:value-of select="."/></font>
</xsl:template>

<xsl:template match="ors:year-of-introduction">  
 <xsl:value-of select="."/>
</xsl:template>

</xsl:stylesheet>

When more templates match, the most specific gets executed

Matching attributes

match with @attribute
name/@attribute matches the attribute of elements with name"name"
name[@attribute] matches the element name with atttribute "attribute"
name[@attribute = 'value'] matches element "name" only if it has attribute "attribute" with "value"

Template selections

<xsl:apply-templates select="name" > explicit call to template
May be used more than once in different places of the stylesheet
<xsl:value-of select="name" >
Includes the evaluated content of "name" in the output
All tags removed, entities resolved

Attributes in the output

Create <a href="http://www.iie.nl">http://www.iie.nl</a>
From: <website>http://www.iie.nl</website>

Using

<a href="<xsl:value-of select='website'>">website</a>

Is illegal: in XML no elements allowed in attributes

<a href="{website}">website</a>

does the job

Reuse the same elements with different templates

Sometimes the same elements have to be processed in different ways
Create Table-of-Contents or List-of-References
Use template with mode-attribute
<apply-templates select="title" mode="ToC"/ >
<apply-templates select="title" mode="Contents"/ >

Using mode-attribute on xsl:template

<xsl:template match="Contributions">
<ol>
<apply-templates select="Contribution" mode="ToC"/ >
</ol>

<apply-templates select="Contribution" mode="Contents"/ >  

</xsl:template>

 
<xsl:template match="Contribution" mode="ToC" >
<li><xsl:value-of select="Title" /> </li> 
</xsl:template>


<xsl:template match="Contribution" mode="Contents" >
<h1><xsl:value-of select="Title" /> </h1> 
<xsl:apply-templates select="Content" /> 
</xsl:template>

Conditional processing

If statement (no else):

  <xsl:if test="$condition">
  <xsl:text>print this text</xsl:text>
</xsl:if>

Choose among alternatives with <xsl:when> and <xsl:otherwise>:

<xsl:choose>
  <xsl:when test="$count > 2"><xsl:text>, and </xsl:text></xsl:when>
  <xsl:when test="$count > 1"><xsl:text> and </xsl:text></xsl:when>
  <xsl:otherwise><xsl:text> </xsl:text></xsl:otherwise>
</xsl:choose>

Defining variables

<xsl:variable> allows you to associate a variable with a string, node list, or result tree fragment
Variables are "single assignment"
You cannot change them
Advantage: no side effects
Variables are lexically scoped
For instance used inside an if statement, they do no exist outside

Using variables

Once assigned, variables can be used in XSL element attributes and templates
XSL element attributes that expect an expression
Attribute value templates: in the form "{$variable}"

Counting and numbering

<xsl:number> can be used for counting and numbering

It can evaluate an expression and format it

     <xsl:number value="6+1" format="A. "/>

It can be used to count the number of elements and format them

<xsl:number count="iteminlist" format="i. "/>
<xsl:number count="chapter" from="manual" level="any" format="1. "/>
<xsl:number count="h1|h2|h3" level="multiple" from="chapter|appendix" format="1."/>

Many more possibilities to format the output

An elaborate example

Check-out the follwoing files for a longer examples
An XML-file describing a music collection
An XSL-file
The result html-file

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