XSLT: crash course
or
Programming Language Design Principle
http://www-sato.cc.u-tokyo.ac.jp/schuko/
XSLT-intro.ppt
10, Jun, 2004
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Why XSLT ?
• Very Simple to Parse (just XML),
a little Harder than Scheme
• A Typical Programming Language on XML
Informal Semantics, but well Described.
• XSLT Processors at Hand!
No Need of Installation. (MSXML)
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References
• XSLT Programmer’s Reference
Michael Kay, WROX Press, 2001
• XSLT
Doug Tidwell, O’Reilly, 2001
• XSLT Cookbook
Sal Mangano, O’Reilly, 2002
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What is XSLT?
• eXtensible Stylesheet Language
Transformation
A transformation expressed in XSLT
describes rules for transforming a source
tree into a result tree.
Show by Example:
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Why XSLT Designed?
• Requirements of XML
o Separating Data from Presentation
o Transmitting Data between
Applications.
•  XML Fixed, and
Transformer Designed  XSLT
(to HTML, PDF, …)
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Systems for XML Handling
• XSLT
• XQuery
 XML as Semi-Structured DataBase
Rigid Formal Semantics is Given with
Type System.
• XPath
 Navigation in XML
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How XSLT Works
• A transformation expressed in XSLT
describes rules for transforming a source
tree into a result tree.
XML
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XML
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How XSLT Works? (2)
• The transformation is achieved by
associating patterns with templates.
Patterns in Templates:
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Template
Match
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How XSLT Works (3)
• A pattern is matched against elements in the
source tree.
• A template is instantiated to create part of
the result tree.
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In Summary,
• A transformation expressed in XSLT is
called a stylesheet. This is because, in the
case when XSLT is transforming into the
XSL formatting vocabulary, the
transformation functions as a stylesheet.
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StyleSheet – A Key Idea
• A stylesheet contains a set of
template rules.
A template rule has two parts:
(1) a pattern which is matched against nodes
in the source tree and
(2) a template which can be instantiated to
form part of the result tree.
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Execution Model
• The result tree is constructed by
(1) finding the template rule for the
root node and
(2) instantiating its template.
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Instantiating a Template
• When a template is instantiated, each
instruction is executed and replaced by the
result tree fragment that it creates.
contents of template =
Instructions (explained later)
Literal Result Element(Data)
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Instantiating a Template (2)
• Instructions can select and process
descendant source elements.
• Processing a descendant element creates a
result tree fragment by finding the
applicable template rule and instantiating its
template.
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Programming Style (Digression)
• Push Processing
-- Just call <xsl:apply-templates/>
Execution
(1) Select All Children,
(2) Push Them to the Stylesheet, and
(3) Let the Stylesheet Select Appropriate
Templates
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Programming Style (2)
• Pull Processing
-- Select a Class of Specific Nodes as
<xsl:apply-templates select=“…”/>
Execution
(1) Select Specific Nodes,
(2) Pull a Specific Template for their
Processing
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Key Ideas in Execution
• Execution by Template Instantiation
• Elements are only processed when they
have been selected by the execution of an
instruction.
 Selection Schema is Critical
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Templates, Expressions, Datatypes
• So much for Templates
 Templates = Functions in Traditional
Sense.
• Remaining Part of Programming Languages
 Expressions and Datatypes
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Variable and Binding
• Form:
<xsl:variable name=… select=…/>
• The Same as Traditional Variables
name = (value of select)
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Example of XSL:VARIABLE
<xsl:variable name=
"para-font-size">12pt</xsl:variable>
<xsl:template match="para">
<fo:block font-size=
"{$para-font-size}">
<xsl:apply-templates/>
</fo:block>
</xsl:template>
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• <xsl:param …/>
Another Mechanism for Binding a Value to
a Variable.
-- Parameters of Template
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Example of Parameters
<xsl:template name="numbered-block">
<xsl:param name="format">1.</xsl:param>
<fo:block>
<xsl:number format="{$format}"/>
<xsl:apply-templates/>
</fo:block>
</xsl:template>
<xsl:template match="ol//ol/li">
<xsl:call-template name="numbered-block">
<xsl:with-param name="format">a.
</xsl:with-param>
</xsl:call-template>
</xsl:template>
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Scope of Variables
• Ordinary Rules for Scope.
Does not Exceed the Extent of Template.
From the Binding Point to the Point that
Another Value is bound to the same name
Variable.
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To See the Result…
• Call factorial with the XML file:
<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl"
href="fac.xsl"?>
<root>
100
</root>
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What is VALUE?
• Factorial isn’t Everything.
• Expression and Datatype to Represent XML
Tree Structure.
Boolean, Number, String (Ordinary)
+
NodeSet
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XPath
• Defines Expressions and their Expressive
Power.
• Ordinary Boolean, Number, String
• Variable Reference, Function Call
• Path Expressions Specifying Node-Sets.
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Node-Set in XPATH
• Selecting a Subset of a Tree.
• Traversing a Tree, and Specifying
Conditions of the form STEP:
Axis:: NodeTest [Predicates]
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Ancestor
Preceding
Self
Following
Descendant
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XPATH Syntax (2)
• Abbreviations:
(frequently used axis)
// -- /decendant-or-self::
@ -- /attribute::
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XPATH Syntax
• Basic Form
[/]Step/Step/Step/…/Step
Step ≡ Axis::Node-Set ([ Predicate ]?)
Axis ≡ self | child | descendant | parent
| ancestor | sibling |
following- sibling | following |
preceding-sibling | preceding |
attribute | …
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Examples of LocationPATH
//figure
@title
book/author/first-name
para[3]
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Control Structure of XSLT
• Conditional
<xsl:if test=…>
<xsl:choose>
<xsl:when test=…>
<xsl:otherwise>
• Jump
<xsl:apply-templates match=…>
<xsl:call-template name=…>
<xsl:for-each>
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Control Structure of XSLT (2)
• Note XSLT has NO ITERATION.
• ITERATION must be written in
Recursion.
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General Theory in Design
• Design of Programming Language
⇔ Model of Computing
o Machine (CPU and memory)
o Object Interaction
o Recursion Thoery
o λ-Calculus
o Term Rewriting
o…
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Model of Computing
• Goal 1:
Representing Key Concepts of Computing
o functional language  function
o OO language  object
Objects for “Key Concepts” must be treated
as a FIRST CLASS OBJECT.
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Model of Computing (2)
• Goal 2:
Representing Control
o Control Structure (Conditional)
o Subroutine Call
o Data Structure
They can Make Overlap.
Object, Type, Class
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XSLT Execution Model
• Tree Manipulation
Node Selection by XPATH Expression
Basic Control Structure Given as
<xsl:if>
<xsl:choose> <xsl:when>
<xsl:apply-templates>
<xsl:call-template>
Tree Construction in XML way.
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