How It Works
October 30, 2000
In Step 1, we specified an XSL style sheet. The first couple of lines
are standard boilerplate:
<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/TR/WD-xsl">
They specify the version of XML and the namespace for the XSL style sheet.
The next line is more important:
<xsl:template match="/">
This "/" string indicates that the following template should be
applied to the root node of the XML document, i.e. to all of it.
The next dozen or so lines (beginning with <html> and ending
with </html>) define the XHTML template. Within this template
are some XSL instructions for extracting data from the XML document.
Look at the <title> element:
<title>Film Library:<xsl:value-of
select="filmlibrary/name"/></title>
The <xsl:value-of> element says that we want to use the element
content for the element that matches the value of the select
attribute. In this case, we are going to use the value of the
<name> element that is a child of the <filmlibrary>
element.
Thus:
<title>Film Library:<xsl:value-of
select="filmlibrary/name"/></title>
gets transformed into:
<title>Film Library:Classic Films</title>
because 'Classic Films' is the content of then <name> tag
contained within the <filmlibrary> tag in the XML file:
<filmlibrary>
<name>Classic Films</name>
That is, <xsl:value-of select="filmlibrary/name"/> is replaced
with Classic Films because 'Classic Films' is the value of the
"filmlibrary/name" selection used in the <xsl:value-of>
element. (One may think of it almost as a programmed find-and-replace
technique.)
The next occurrence of an XSL element is in the <table> element:
<xsl:for-each select="filmlibrary/movie">
The <xsl:for-each> element instructs the browser that we want
to repeat the following template for each occurrence of the element
which matches the value of the select attribute. In this case, we are
going to repeat the template for each <movie> element that is a
child of the <filmlibrary> element.
Within this for-each loop are a set of <xsl:value-of> elements
which put the value of the <title>, <director>,
<year>, and <genre> elements into the table:
lt;tr>
lt;td><xsl:value-of select="title"/></td>
lt;td><xsl:value-of select="credits/director"/></td>
<td><xsl:value-of select="year"/></td>
<td><xsl:value-of select="genre"/></td>
</tr>
So even though we have two <movie> elements within our XML
file, we only need the one <xsl:for-each> block in our XSL file
to perform the same operation on both the <movie> elements.
Obviously, we could have as many <movie> elements as we wanted
in our file and we would still need only one <xsl:for-each>
element to process all of them.
In Step 2, we authored the XML document. Like the XML style sheet,
the first line indicates the version of XML that we are using:
<?xml version="1.0"?>
The second line associates the style sheet with our XML document:
<?xml-stylesheet type="text/xsl" href="movie1.xsl"?>
The rest of the document contains the content that gets transformed
by the XSL style sheet.
In Step 5, we create a second XSL style sheet. Looking at the first
couple of lines in this style sheet:
<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/TR/WD-xsl">
<xsl:template match="/">
we see the same XML version and XSL style sheet namespace
identifiers, as well as the <xsl:template> element, as in the
previous sheet.
Where this style sheet departs from the previous one is that rather
than formatting the XML document as a table, we format it using
headers and paragraphs.
Looking at the <body> element, we wrote:
<body>
<xsl:for-each select="filmlibrary/movie">
This means that the element content of the <body> element will
be based on each occurrence of the <movie> element in our XML
document.
The <h1> element is defined by the following lines of XML:
<h1 style="text-align: center">
<xsl:value-of select="title"/>
</h1>
The <xsl:value-of> element means that the <h1> element
will contain the content of the <title> element. Similarly, the
<h2> element will contain the content of the <year> and
<director> elements:
<h2 style="text-align: center">
<xsl:value-of select="year"/> <xsl:
value-of select="credits/director"/>
</h2>
[Note: The 2nd and 3rd lines above are one line. They were split for
formatting purposes]
and the <p> element will contain the content of the
<genre> and <plot> elements:
<p>
<xsl:value-of select="genre"/>.<xsl:value-of select="plot"/>
</p>
In Step 7, we associate the style sheet with the XML document:
<?xml-stylesheet type='text/xsl' href='movie2.xsl'?>
When we load the XML document into Microsoft Internet Explorer, the
document is then transformed using the associated style sheet.
Summary
In this chapter, we learned a little about media types:
- Using media types to manage different types of web devices
- Managing media types using the <style> element
- Managing media types using the <link> element
- Controlling how documents are printed using @media and @page rules
- Forcing page breaks with page breaking properties
We also learned about three types of problems affecting our ability
to target different devices:
- Device constraints
- User agent constraints
- Human interface device constraints
Finally, we introduced some strategies for overcoming these
constraints. We can author different versions of our content for
different devices, use tools that adapt content to different devices,
or generate content based on the type of device.
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Title:
Beginning XHTML
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ISBN: 1861003439
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US Price: $ 39.99
Canadian Price: C$ 59.95
UK Price: £ 28.99
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Publication Date: Mar 00
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Pages: 733
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©1999
Wrox Press Limited, US and UK.
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Using XSL Transformations
Beginning XHTML
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