Transcript Slide 1
Extensible Stylesheet
Language (XSL)
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XHTML
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XHTML
• XHTML stands for EXtensible HyperText Markup
Language
• XHTML is aimed to replace HTML
• XHTML is almost identical to HTML 4.01
• XHTML is a stricter and cleaner version of HTML
• XHTML is HTML defined as an XML application
• XHTML is a W3C Recommendation
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HTML Vs. XHTML
• The Most Important Differences:
- XHTML elements must be properly nested
- XHTML documents must be well-formed
- Tag names must be in lowercase
- All XHTML elements must be closed
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XML Namespaces
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XML Namespaces
• When an element name appears in two different
XML documents, we would like to know that it
has the same meaning in both documents
- Is the tag <title> used as the <title> XHTML tag in
both documents?
- If two documents about books have the tag
<number>, does it mean that they use the same
system for cataloging books?
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What XML Namespaces are
and What They are not
• Namespaces merely provide a mechanism for
creating unique names (for elements and
attributes) that can be used in XML documents all
over the Web
- A namespace is just a collection of names that were
created for a specific domain of applications
• Namespaces are not DTDs and they do not
provide a mechanism for validation of XML
documents using multiple DTDs
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Identifying an XML Namespace
• A name space is identified by a URI
• The URI does not have to point to anything
- It is merely used as a mechanism for creating unique
names
• An element name or attribute name from a
namespace has two parts
prefix identifies
the namespace
prefix:name
name is just a
name from the
namespace
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Recognizing Namespace
• When an application sees a qualified name, it
may recognize it and act accordingly
- A browser identifies tags that belong to the XHTML
namespace and processes them
- An XSLT processor identifies tags and attributes that
belong to the XSLT namespace and executes them
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Declaring a Namespace
• An XML namespace is declared in the xmlns
attribute
<foo:book xmlns:foo=“http://www.foo.org/”>
<foo:title> XML Namespaces </foo:title>
<foo:author> John Doe </foo:author>
</foo:book>
Using foo as the prefix, instead of using the
URI, is more convenient
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The Default Namespace
• The default namespace is declared without a
prefix
<book xmlns=“http://www.foo.org/”>
<title> XML Namespaces </title>
<author> John Doe </author>
</book>
All the above elements belong to the
default namespace
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DTDs as Namespaces
• The URI of a namespace may point to a DTD
• A DTD defines a namespace comprising all its
element names and attribute names
- But it is just a namespace – not a DTD!
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This document is
invalid according
to either DTD!
<bib:book
Example
xmlns:bib=“http://www.acm.org/bibliography.dtd”
xmlns:isbn=“http://www.isbn-org.org/def.dtd”>
<bib:title> Proceedings of SIGMOD </bib:title>
<bib:number> 472010 </bib:number>
<isbn:number> 1-58113-332-4 </isbn:number>
</bib:book>
But the document is well formed! (e.g., in the
book element, attribute names are unique)
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Alternatively, One Namespace can be
Declared as the Default
<book
xmlns=“http://www.acm.org/bibliography.dtd”
xmlns:isbn=“http://www.isbn-org.org/def.dtd”>
<title> Proceedings of SIGMOD </title>
<number> 472010 </number>
<isbn:number> 1-58113-332-4 </isbn:number>
</book>
This document is well formed but
invalid according to either DTD!
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Scope of Namespaces
• The scope of a namespace declaration is the
element containing the declaration and all
descendant elements
- Must use the prefix anywhere in the scope
• Only the default namespace can be
redeclared
• More than one namespace can be declared in
the same scope
- At most one can be the default namespace
- All others must have unique prefixes
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What about Attributes?
• Recall that element names and attribute names must
be qualified if they belong to a nondefault namespace
• Unqualified element names belong to the default
namespace (if they are inside the scope)
• However, an unqualified attribute does not belong to
the default namespace
• An unqualified attribute is processed according to the
rules that apply to its element name
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Extensible Stylesheet
Language (XSL)
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XSL
XSL is a standard that consists of three parts:
• XPath (navigation in documents)
• XSLT (transformation of documents)
• XSLFO (FO for formatting objects)
- This is a rather complex language for typesetting (i.e.,
preparing text for printing)
- It will not be taught
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XSL Transformations (XSLT)
An Example
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XSLT
• XSLT is a language for transforming XML
documents into other XML documents
- For example, XHTML, WML
- Can also transform XML to text documents
• An XSLT program is itself an XML document
(called an XSL stylesheet) that describes the
transformation process for input documents
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XSLT Processors
DTD
XML
XSL
XHTML
WML
XSLT Processor
Text
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Web Pages – The Whole Picture
Knowledge
XSL
XHTML
XML
Data
Doc.
Structure
CSS
Style
Layout
Web Page
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<?xml version="1.0" encoding="ISO-8859-1"?>
<catalog>
<cd country="UK">
<title>Dark Side of the Moon</title>
<artist>Pink Floyd</artist>
<price>10.90</price>
</cd>
<cd country="UK">
<title>Space Oddity</title>
<artist>David Bowie</artist>
<price>9.90</price>
</cd>
<cd country="USA">
<title>Aretha: Lady Soul</title>
<artist>Aretha Franklin</artist>
<price>9.90</price>
</cd>
catalog.xml
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</catalog>
Valid XML!
Commands are XML elements
Includes XHTML with the namespace xsl
elements
<?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>
<head><title>cd catalog</title></head>
<body><h1>This is a cd catalog!</h1></body>
</html>
</xsl:template>
</xsl:stylesheet>
catalog.xsl
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Applying XSL Stylesheets to XML
There are several ways of applying an XSL
stylesheet to an XML document:
- Directly applying an XSLT processor to the XML
document and the XSL stylesheet
- Calling an XSLT processor from within a program
- Adding to the XML document a link to the XSL
stylesheet and letting the browser do the
transformation
• The resulting XHTML document is shown instead
of the original XML
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How Does XSLT Work?
• An XSL stylesheet is a collection of templates that are
applied to source nodes (i.e., nodes of the given XML)
• Each template has a match attribute that specifies to
which source nodes the template can be applied
• Each source node has a template that matches it
• The current source node is processed by applying a
template that matches this node
• When processing a node, it is possible (but not
necessary) to recursively process other nodes, e.g., the
children of the processed node
• The XSLT processor processes the document root (/)
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Templates
• A template has the form
<xsl:template match="pattern">
...
</xsl:template>
• The content of a template consists of
- XML elements (e.g., XHTML) and text that are
copied to the result
- XSL elements (<xsl:…>) that are actually
instructions
• The pattern syntax is a subset of XPath
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<?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>
<head><title>cd catalog</title></head>
<body><h1>This is a cd catalog!</h1></body>
</html>
</xsl:template>
</xsl:stylesheet>
catalog1.xsl
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<?xml version="1.0" encoding="ISO-8859-1"?>
<?xml-stylesheet type="text/xsl"
href="catalog1.xsl"?>
<catalog>
<cd country="UK">
<title>Dark Side of the Moon</title>
<artist>Pink Floyd</artist>
<price>10.90</price>
</cd>
<cd country="UK">
<title>Space Oddity</title>
<artist>David Bowie</artist>
<price>9.90</price>
</cd>
<cd country="USA">
<title>Aretha: Lady Soul</title>
<artist>Aretha Franklin</artist>
<price>9.90</price>
</cd>
</catalog>
catalog1.xml
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The Result
<html>
<head>
<META http-equiv="Content-Type"
content="text/html; charset=UTF-8">
<title>cd catalog</title>
</head>
<body>
<h1>This is a cd
Automatically
catalog!</h1>
added to <head>
</body>
</html>
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Examples of Match Attributes
• match="cd",
- All elements with tag name cd
• match="//cd",
match="/catalog/cd/artist"
- All matches of the absolute XPath
• match="cd/artist"
- All artist nodes that have a cd parent
• match="catalog//artist"
- All artist nodes that have a catalog ancestor
• match="cd[@country='UK']/artist"
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<xsl:apply-templates>
• Processing starts by applying a template to the root
- If no specified template matches the root, then one is
inserted by default (see the next slide)
• The XSL stylesheet must specify explicitly whether
templates should be applied to descendants of a node
• It is done by putting inside a template the instruction:
<xsl:apply-templates select="xpath"/>
- In xpath, the current processed node is used as the
context node
• Without the select attribute, this instruction
processes all the children of the current node
(including text nodes)
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Default Templates
• XSL provides implicit built-in templates that match
every element and text nodes
<xsl:template match="/|*">
<xsl:apply-templates/>
</xsl:template>
<xsl:template match="text()|@*">
<xsl:value-of select="."/>
</xsl:template>
• Templates we write always override these built-in
templates (when they match)
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<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
</xsl:stylesheet>
Dark Side of the Moon
Pink Floyd
10.90
Space Oddity
David Bowie
9.90
…
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<?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="cd">
<h2>A cd!</h2>
</xsl:template>
</xsl:stylesheet>
<h2>A cd!</h2>
<h2>A cd!</h2>
<h2>A cd!</h2>
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<?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="cd[@country='UK']">
<h2>A cd!</h2></xsl:template>
</xsl:stylesheet>
<h2>A cd!</h2>
<h2>A cd!</h2>
Aretha: Lady Soul
Aretha Franklin
9.90
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<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
<xsl:apply-templates
select="catalog/cd[@country='UK']/artist"/>
</xsl:template>
<xsl:template match="artist">
<h2>An artist!</h2>
</xsl:template>
</xsl:stylesheet>
<h2>An artist!</h2>
<h2>An artist!</h2>
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<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
<xsl:apply-templates
select="cd[@country='UK']/artist"/>
</xsl:template>
<xsl:template match="artist">
<h2>An artist!</h2>
</xsl:template>
</xsl:stylesheet>
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The Most Frequently Used
Elements of XSL
• <xsl:value-of select="xpath"/>
- This element extracts the value of a node from the
node list located by xpath
• <xsl:for-each select="xpath"/>
- This element loops over all the nodes in the node
list located by xpath
• <xsl:if test="cond"/>,
<xsl:if test="xpath"/>, etc.
- This element is for conditional processing
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<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet version="1.0"
Example 1
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
<html><head><title>cd catalog</title></head>
<body>
<h1>CD catalog</h1>
Currently selected element is
the context (current) node
<ul>
<xsl:for-each select="catalog/cd">
<li><xsl:value-of select="title"/>
[<xsl:value-of select="artist"/>]</li>
</xsl:for-each>
</ul></body></html>
</xsl:template>
</xsl:stylesheet>
catalog2.xsl
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Example 2
<?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><head><title>cd catalog</title></head>
<body>
<h1>CD catalog</h1>
<ul>
<xsl:for-each select="catalog/cd">
<li><xsl:apply-templates select="."/></li>
</xsl:for-each>
</ul></body></html>
</xsl:template>
catalog3.xsl
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Example 2
(cont.)
Entities replace characters
<xsl:template match="cd">
Price<10 → price<10
<b><xsl:value-of select="artist"/></b>:
<xsl:value-of select="title"/>
<xsl:if test="price<10">
(<em>now on sale: $<xsl:value-of select="price"/>
</em>)
</xsl:if>
</xsl:template>
</xsl:stylesheet>
catalog3.xsl
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<xsl:choose>:
Switch syntax for conditions
Example 3
<xsl:choose>
<xsl:when test="price < 9">
<em>Special price!</em>
</xsl:when>
<xsl:when test="price>9 and price<=10">
<i>Good price!</i>
</xsl:when>
<xsl:otherwise>
(Normal price.)
</xsl:otherwise>
</xsl:choose>
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The <xsl:sort> Element
• The <xsl:sort> element is used to sort the
list of nodes that are looped over by the
<xsl:for-each> element
• Thus, the <xsl:sort> must appear inside the
<xsl:for-each> element
• The looping is done in sorted order
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<?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><head><title>cd catalog</title></head>
<body>
<h1>CD
CDs are iterated in ascending
order of the titles
catalog</h1>
<ul>
<xsl:for-each select="catalog/cd">
<xsl:sort select="title"/>
<li><xsl:value-of select="title"/></li>
</xsl:for-each>
</ul></body></html>
</xsl:template>
</xsl:stylesheet>
catalog4.xsl
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Setting Values in Attributes
• The <xsl:value-of> element cannot be used
within attribute value
• However, we can insert expressions into attribute
values, by putting the expression inside curly
braces ({})
• Alternatively, we can use <xsl:element> in
order to construct XML elements
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An Example
• In the following example, we add to each CD entitled t a
link to the URL /showcd.php?title=t
<xsl:template match="cd">
<b><xsl:value-of select="artist"/></b>:
<a href="/showcd.php?title={./title}">
<xsl:value-of select="title"/>
</a>
</xsl:template>
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Using <xsl:element>
<xsl:template match="cd">
<b><xsl:value-of select="artist"/></b>:
<xsl:element name="a">
<xsl:attribute name="href">
showcd/?title=<xsl:value-of select="title"/>
</xsl:attribute>
<xsl:value-of select="title"/>
</xsl:element>
</xsl:template>
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On XSL Code
• Typically, an XSLT program can be written in
several, very different ways
- Templates can sometime replace loops and vice versa
- Conditions can sometimes be replaced with XPath
predicates (e.g., in the select attribute) and vice versa
• A matter of convenience and elegancy
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On Recursive Templates
• It is not always possible to avoid recursive
templates
- That is, use only the template of the root
• Suppose that we want to write an XSL stylesheet
that generates a copy of the source document
- It is rather easy to do it when the structure of the
source XML document is known
• Can we write an XSL stylesheet that does it for
every possible XML document?
- Yes! (see next slide)
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<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="1.0">
<xsl:output method="xml"/>
<xsl:template match="*">
<xsl:element name="{name()}">
<xsl:for-each select="@*">
<xsl:attribute name="{name()}">
<xsl:value-of select="."/>
</xsl:attribute>
</xsl:for-each>
<xsl:apply-templates/>
</xsl:element>
Identity Transformation
</xsl:template>
</xsl:stylesheet>
Stylesheet
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Generating Valid XHTML
• By default, the documents that XSL stylesheets
generate are not valid XHTML
• Next, we will show how XSL stylesheet can be
changed in order to generate valid XHTML
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The Original XSL 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>
<head><title>cd catalog</title></head>
<body><h1>This is a cd catalog!</h1></body>
</html>
</xsl:template>
</xsl:stylesheet>
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The Original Transformation Result
<html>
<head>
No DOCTYPE
<META http-equiv="Content-Type"
content="text/html; charset=UTF-8">
<title>cd catalog</title>
</head>
<body>
<h1>This is a cd
Uppercase tag name,
catalog!</h1>
unclosed element
</body>
</html>
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Modifying the XSL Example
<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns="http://www.w3.org/1999/xhtml">
<xsl:output
method="html"
doctype-public="-//W3C//DTD XHTML 1.0 Strict//EN"
doctype-system=
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"/>
<xsl:template match="/"> …
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The Transformation Result
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0
Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>cd catalog</title>
</head>
<body>
META is not inserted
<h1>This is a cd catalog!</h1>
</body>
</html>
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Some Other XSL Elements
• The <xsl:text> element inserts free text
in the output
• The <xsl:copy-of select="xpath">
creates a copy of the specified nodes
• The <xsl:comment> element creates a
comment node in the result tree
• The <xsl:variable> element defines a
variable (local or global) that can be used
within the program
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W3Schools Tutorial on XSLT
• The W3Schools XSLT Tutorial has (among other
things) tables that list all the elements and
functions of XSLT
• It also has some details about implementations
- Some browsers may not implement all features or
may implement some features differently from the
specifications
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The End!
These slides are based on those developed for the course:
http://www.cs.huji.ac.il/~dbi
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