XSL Transformation

1
XSL Transformation
2
Introduction
3
Why Styling?

• XML
• Concentrate on structure
• Not concentrate on appearance
• To View XML documents, we need to format or style
  them
• The styling is directly related to and derived
  from the structure of the document
• Two W3C styling sheets
• CSS Cascading Styling Sheet
• XSL XML Style-sheet Language

4
Cascading Style Sheet (CSS)

• Originally for HTML
• A set of rules that tell the browser which font,
  style, and margin to use to display the text

• section.title
• font-family Garamond, Time News Roman,
  serif
• font-size 10pt
• margin5px
• displayblock
• font-style italic

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XML Stylesheet Language (XSL)

• Support transforming the document before display
• A transformation language
• A formatting language

• ltPgtltBgt Table of Content lt/Bgtlt/Pgt
• ltULgt
• ltxslfor-each select article/section/titlegtltLI
  gtltAgt
• ltxslvalue-of select./gt lt/Agtlt/LIgt
• lt/xslfor-eachgt
• lt/ULgt

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XSL

• XSLT XSL Transformation
• a language for transforming XML documents into
  other XML (or non XML) documents.
• Electronic commerce, Electronic data exchange,
  Metadata change
• XSLFO XSL Formatting Objects
• XML vocabulary for specifying formatting
• XSLFO and CSS are very similar in scope

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XSL Processors

• Xalan (include Java Version and C Version)
• http//xml.apache.org/xalan-c/
• James Clark
• www.jclark.com

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Concepts of XSLT
Source Document
Resulting Document
XSLProcessor
XSLT Style Sheet
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Concept of XSLT (Cont.)

• XSLT A language to specify transformation of XML
  documents
• Add elements specifically for viewing
• Add the logo or address of the company
• Create new content from an existing one
• Create table of content
• Create views for different users
• Convert between different DTDs
• Transform XML documents into HTML

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Concept of XSLT (Cont.)

• A transformation in the XSLT language is
  expressed as a well-formed XML document
  conforming to the Namespaces in XML
  Recommendation which may include both elements
  that are defined by XSLT and elements that are
  not defined by XSLT.
• XSLT-defined elements are distinguished by
  belonging to the XSLT namespace.
• XSLT namespace http//www.w3.org/1999/XSL/Transfo
  rm
• xmlnsxslhttp//www.w3.org/1999/XSL/Transform

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Concept of XSLT (Cont.)

• A transformation expressed in XSLT describes
  rules for transforming a source tree into a
  result tree.
• The transformation is achieved by associating
  patterns with templates.
• A pattern is matched against elements in the
  source tree.
• A template is instantiated to create part of the
  result tree.
• The result tree is separate from the source tree.
  
• In constructing the result tree, elements from
  the source tree can be filtered and reordered,
  and arbitrary structure can be added.

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Concept of XSLT (Cont.)

• A transformation expressed in XSLT is called a
  stylesheet
• A stylesheet contains a set of template rules. A
  template rule has two parts
• A pattern which is matched against nodes in the
  source tree
• A template which can be instantiated to form part
  of the result tree

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Concept of XSLT (Cont.)

• XSLT transforms one XML tree into another
• select particular nodes from the input tree
• reorder/process nodes
• output nodes

• Tree nodes
• The root
• Elements
• Text
• Attributes
• Namespaces
• Processing instructions
• Comments

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Basic XSLT
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Example Scenario

• An XML document describing two people 8-1.xml
• Basic XSLT
• XSLT is a well-formed XML document
• The tree of the source document
• The tree of the resulting document
• How to transform one into the other
• The root of this document is stylesheet
• In the http//www.w3.org/1999/XSL/Transform name
  space
• xmlnsxslhttp//www.w3.org/1999/XSL/Transform
• xslstylesheet

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An Minimal XSLT Stylesheet

• 8-1.xsl
• The output consists of a text declaration plus
  the text of the input document
• The net effect of applying an empty stylesheet to
  any input XML document is to reproduce the
  content but not the markup of the input document
• Built-in rules

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Using Xalan

• Xalan is an XSLT processor that reads an XSLT
  stylesheet and an input XML document, and builds
  an output document by applying the instructions
  in the stylesheet to the information in the input
  document
• Set up the Xalan Environment
• Download Xalan-C and Xerces-C
• Set path
• Path D\Package\xerces-c_2_3_0-win32\bin
  d\package\xml-xalan\c\Build\Win32\VC6\Release
  C\WINNT\system32C\WINNTC\WINNT\System32\Wbem
  
• Use Xalan
• Xalan -o outputfile xmlSource stylesheet

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The xml-stylesheet Processing Instruction

• XML documents that will be served directly to web
  browsers can have an xml-stylesheet PI in their
  prolog telling the browser where to find the
  associated stylesheet for the document
• 8-2.xml lt?xml-stylesheet type"text/xsl"
  href"./8-1.xsl" ?gt

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Templates and Template Rule

• To control what output is created from what
  input, you add template rules to the XSLT
  stylesheet
• Each template rule is represented by an
  xsltemplate element
• This element has a match attribute that contains
  an XPath pattern identifying the input it matches
• Its content lists the elements to be inserted in
  the output
• Example
• ltxsltemplate matchpersongtA Personlt/xsltemplat
  egt
• 8-2.xsl literal data characters
• 8-3.xsl literal result elements

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Calculating the Value of an Element with
xslvalue-of

• xslvalue-of takes the value of something and
  copies it into the output document
• The value of a node is always a string
• Value of an element node concatenation of all
  the parsed character data (but not markup)
  between its start and end tag
• The element whose value is taken is identified by
  a select attribute containing an XPath expression
• 8-4.xsl

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Path

• XML path is similar to file paths
• Start from the root of an XML document
• Elements are separated by /
• The root is a node before the top-level element
• Path Tips
• / immediate children of a node
• /article/title
• // all the descendant from a node
• /article//title
• wildcard character (/article/)
• or character (title p)
• XPath recommendation (http//www.w3.org/TR/xpath)

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Wildcards

• Asterisk () matches any element node regardless
  of name
• does not match attributes, text nodes,
  comments, or processing-instruction nodes
• You can put a namespace prefix in front of
  (svg)
• node() wildcard matches not only all element
  types, but also text nodes, comments,
  processing-instruction nodes, and attribute nodes
• _at_ matches all attribute nodes
• _at_xlink (namespace)

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Path Example
root
/
/article
article
title
date
abstract
keyword
section
/article/title
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Applying Templates with xslapply-templates

• By default, an XSLT processor reads the input XML
  document from top to bottom, starting at the root
  of the document and working its way down using
  preorder traversal
• Template rules are activated in the order in
  which they match elements encountered during this
  traversal
• A template rule for a parent will be activated
  before template rules matching the parents
  children
• The xslapply-templates element lets you make
  explicit choice of processing order
• Its select attribute contains an XPath expression
  telling the XSLT processor which nodes to process
  at that point in the output tree
• 8-5.xsl, 8-6.xsl, 8-7.xls

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Actions of XSL Processor

• Load the style sheet
• Load the source document
• Walk through the source document from root to
  leaf
• Match the current node against a template
• If match, generates the node in the resulting
  tree
• Encounter ltxslapply-templatesgt
• Move to the children of the current node and
  repeat the process

Recursive call to the Stylesheet
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The Built-in Template Rules

• ltxsltemplate match / gtltxslapply-template
  s /gtlt/xsltemplategt
• ltxsltemplate match"text()_at_"gt ltxslvalue-of
  select"."/gtlt/xsltemplategt
• ltxsltemplate match"processing-instruction()comm
  ent()"/gt
• A simple template rules matches namespace nodes
  and instructs the processor not to copy any or
  part of the namespace node to the output

Whenever a text or attribute node is matched ?
output the node value
Note by default the XSLT processor never reaches
attribute nodes, unless a specific rule applies
templates to them
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Modes

• Sometimes the same input content needs to appear
  multiple times in the output, formatted according
  to a different template each time
• Both xslapply-templates and xsltemplate
  elements can have optional mode attributes that
  connect different template rules to different
  uses
• A mode attribute on xsltemplate identifies in
  which mode that template rules should be
  activated
• An xslapply-templates with a mode attribute only
  activates template rules with matching mode
  attribute
• 8-8.xsl

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Second Example Scenario

• A monthly e-zine, Pineapplesoft Link
• E-mail to subscribers
• Post a copy on Web
• Use one document structure
• XML (e-zine.xml)
• Two different presentations
• XSLT (e-zine.xsl, e-zine2.xsl)

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Matching on Attributes

• Syntax
• matchelement_at_attributevalue
• matchurl_at_protocolmailto
• lturl protocolmailtogt claven_at_cc.nctu lt/urlgt
• lturl protocolhttpgt http//. lt/urlgt
• matchelement_at_attribute
• matchurl_at_protocol
• lturl protocolhttpgt http//. lt/urlgt
• lturlgthttp//www.w3.org lt/urlgt

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Matching Text and Functions

• Functions restrict paths to specific elements
• /article/sectionposition()2/title/text()
• /article/section2/title/text()
• count(//title)

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Matching Text and Functions (Cont.) -- Common XSL
functions

• position()
• the position of the current node in the node set
• text()
• The text (content) of an element
• last()
• the position of the last node in the current node
  set
• count()
• the number of nodes in the current node set
• not()
• negates the argument
• contains()
• return true if the first argument contains the
  second argument
• starts-with()
• return true if the first argument starts with the
  second argument

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Other XSLT Elements

• Named templates
• Numbering and sorting output elements
• Conditional processing
• Iteration
• Extension elements and functions
• Importing other stylesheets

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Creating Nodes in the Resulting Tree

• xslelement
• creates element with a computed name
• xslattribute
• creates attribute with a computed value
• xslattribute-set
• Conveniently combines several xslattribute
• xsltext
• Create a text node
• xslprocessing-instruction
• Create a processing instruction

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Creating Nodes in the Resulting Tree (Cont.)

• xslcomment
• create a comment
• xslcopy
• copies the current node
• xslvalue-of
• computes text by extracting from the source tree
  or inserting a variable
• xslif
• instantiates its content if the expression if
  true
• xslchoose
• select elements to instantiate among possible
  alternatives
• xslnumber
• creates formatted number

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Priority

• Templates with more specific paths take
  precedence over less specific templates
• If conflict between two templates of equivalent
  priority
• Report an error
• Choose the template that appears last in the
  style sheet

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Customized View
XSL Processor
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Advanced XSLT toc.xsl
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Declaring HTML Entities in a Style Sheet

• lt!DOCTYPE xslstylesheet lt!ENTITY copy
  0169gt gt

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Reorganizing the Source Tree

• ltMETA NAME"keywords"gt ltxslattribute
  name"CONTENT"gt ltxslvalue-of
  select"article/keywords"/gt, lt/xslattributegtlt/
  METAgt
• ltMETA NAMEkeywords contentXML, XSL, style
  sheet, publishing, Webgt

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Calling a Template

• Template define with a name
• ltxsltemplate name"title"gt ltxslvalue-of
  select"/article/title"/gt (
• ltxslvalue-of select"/article/date"/gt )
• lt/xsltemplategt
• Call a template
• ltxslcall-template nametitle /gt

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Include a Style Sheet

• ltxslinclude hrefcore.xsl /gt
• xslinclude must be a direct child of
  xslstylesheet

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Repetitions

• ltxslfor-each select"article/section/title"gtltLIgt
  ltAgtltxslattribute name"HREF"gt ltxslvalue-of
  select " generate-id()"/gtlt/xslattributegtltxslv
  alue-of select"."/gtlt/Agtlt/LIgtlt/xslfor-eachgt
• xslfor-each loop over elements
• generate-id() Return a unique identifier for the
  current node

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Related Recommendations

• XSL Transformation (XSLT) http//www.w3.org/TR/199
  9/REC-xslt-19991116
• XML Path (XPath) http//www.w3.org/TR/xpath
• XML Stylesheet http//www.w3.org/TR/xml-stylesheet
  
• Associate stylesheets with XML documents