extensible stylesheet language (xsl)

1

Extensible Stylesheet Extensible Stylesheet Language (XSL)Language (XSL)

2

The XSL StandardThe XSL Standard

XSL consists of 3 parts:

• XPathXPath (navigation in documents)

• XSLTXSLT (transformation of documents)

• XSLFOXSLFO (FO for formatting objects)

- A rather complex language for typesetting

(e.g., for preparing text for printing)- It will not be taught

3

XML Path LanguageXML Path Language(XPath)(XPath)

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XML example revisited: XML example revisited:

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<?xml version="1.0"?>

<!DOCTYPE countries SYSTEM "world.dtd">

<countries>

<country continent="&as;">

<name>Israel</name>

<population year="2001">6199008</population>

<city capital="yes"><name>Jerusalem</name></city>

<city><name>Ashdod</name></city>

</country>

<country continent="&eu;">

<name>France</name>


</country>

</countries> world.xmlworld.xml

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The XML DOM ModelThe XML DOM Model

country

Asia Israel 6199008

name populationcontinent

AshdodJerusalem

namename

2001

year

countries

city

no

capital

yes

capital

city

document rootThe root is implicit(Does not appear in the

text of the XML document)

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<!ELEMENT countries (country*)> <!ELEMENT country (name,population?,city*)> <!ATTLIST country continent CDATA #REQUIRED> <!ELEMENT name (#PCDATA)> <!ELEMENT city (name)><!ATTLIST city capital (yes|no) "no"> <!ELEMENT population (#PCDATA)> <!ATTLIST population year CDATA #IMPLIED> <!ENTITY eu "Europe"> <!ENTITY as "Asia"><!ENTITY af "Africa"><!ENTITY am "America"><!ENTITY au "Australia"> world.dtdworld.dtd

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The XPath LanguageThe XPath Language

• XPath expressions are used for addressing elements (nodes) of an XML document

• Used in XSLT (next subject today) and in XQuery (a query language for XML)

• The syntax resembles that of the Unix file system- But the semantics have some substantial differences

/countries/country[population>10000000]

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<countries>


<name>Israel</name>




</country>


<name>France</name>


</country>

</countries>

world.xmlworld.xml/countries/country[population>10000000]

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<countries>


<name>Israel</name>




</country>


<name>France</name>


</country>

</countries>

world.xmlworld.xml//country[@continent="Asia"]/city

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XPath ExpressionsXPath Expressions

• An XPath expression (or just XPath for short) matches paths in the XML tree

• An absolute path begins with the root of the document- Starts with "/" (or "//")- For example, /countries/country/city, //city

• A relative path begins with a context node that is defined by the application that uses the XPath- For example, city/name, or ./name

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Applying XPath to XMLApplying XPath to XML

• Formally, the result of applying an XPath e to an XML document (or a context node in the

document) is the list of all nodes n in the document, such that e matches the path from the root (or the context node) to n

• The order in the list is defined by the order of the nodes in the document

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XPath Steps and Axis XPath Steps and Axis

• An XPath describes a sequence of steps that together characterize a path

• A step is defined by an axis that specifies a tree relationship between nodes- More particularly, the axis describes how to get from the

current node to the next one- For example, parent-child, child-parent, ancestor-

descendant, etc.

• Consecutive steps are separated by /

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Child AxisChild Axis

• A child axis has the simple form tagName - Go to an element child with the tag tagName

• For example, - /tagName matches the tagName child of root- city/name - /countries/country/city

• The child axis * matches every tag- For example: /*/*/city, */name

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Child-Axis ExamplesChild-Axis Examples

country

Asia Israel 6199008


AshdodJerusalem

namename

2001

year

countries

city

no

capital

yes

capital

city

document root

/countries

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country

Asia Israel 6199008


AshdodJerusalem

namename

2001

year

countries

city

no

capital

yes

capital

city

document root

/countries/country/city

17


country

Asia Israel 6199008


AshdodJerusalem

namename

2001

year

countries

city

no

capital

yes

capital

city

document root

city/name

Context

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country

Asia Israel 6199008


AshdodJerusalem

namename

2001

year

countries

city

no

capital

yes

capital

city

document root

/*/country/*

An attribute is not an element child!

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Self and Descendant-or-Self Self and Descendant-or-Self

• The self axis “.” denotes the identity relationship - That is, the step “remain in the current node”- /countries/country/. ≡ /countries/country- country/./city ≡ country/city

• The descendant-or-self axis means: either stay in the current node or go to some descendant of the current node - descendant-or-self:node(),

• // is a shotrcut notation for /descendant-or-self:node()/- For example, country//name

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Descendant ExamplesDescendant Examples

country

Asia Israel 6199008


AshdodJerusalem

namename

2001

year

countries

city

no

capital

yes

capital

city

document root

/countries//name

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Descendant ExamplesDescendant Examples

country

Asia Israel 6199008


AshdodJerusalem

namename

2001

year

countries

city

no

capital

yes

capital

city

document root

.//*

Context

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Other Axis TypesOther Axis Types

• The parent axis “..” denotes the parent relationship- That is, the step “go to the parent of the current node”- For example, //name/../population

• XPath has more axis types (denoted by a different syntax from the ones shown earlier):- descendant- ancestor- ancestor-or-self- following-sibling- preceding-sibling- …

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Referring AttributesReferring Attributes

• The attribute axis is denoted @attName - That is, “go to the attribute attName of the current node”

• The operator @* matches every attribute

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Attribute ExamplesAttribute Examples

country

Asia Israel 6199008


AshdodJerusalem

namename

2001

year

countries

city

no

capital

yes

capital

city

document root

//country/@continent

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country

Asia Israel 6199008


AshdodJerusalem

namename

2001

year

countries

city

no

capital

yes

capital

city

document root

@continent

Context

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country

Asia Israel 6199008


AshdodJerusalem

namename

2001

year

countries

city

no

capital

yes

capital

city

document root

//@*

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XPath PredicatesXPath Predicates

• Predicates in XPath are used for filtering out steps

• For example, //city[@captial="yes"] will match only capital cities

• Formally, given a predicate [PExpr], the expression PExpr is transformed into a Boolean value and the step is taken only if this value is true- The node reached in the last step is the context node

• XPath has a rather rich language for predicate expressions; we only demonstrate common ones

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<countries>


<name>Israel</name>




</country>


<name>France</name>


</country>

</countries>

world.xmlworld.xml//country[./population>10000000]

• The XPath ./population is transformed into a number by taking its embedded text

• The XPath ./population is relative to the current node (i.e., country) in the path

• Equivalent to //country[population>10000000]

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<countries>


<name>Israel</name>




</country>


<name>France</name>


</country>

</countries>

world.xmlworld.xml//country[.//city]

An XPath evaluates to true if and only if its result is not empty

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<countries>


<name>Israel</name>




</country>


<name>France</name>


</country>

</countries>

world.xmlworld.xml//country[//city]

Why?

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<countries>


<name>Israel</name>




</country>


<name>France</name>


</country>

</countries>

world.xmlworld.xml//country[population[.>3000000 and @year>2003]]

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<countries>


<name>Israel</name>




</country>


<name>France</name>


</country>

</countries>

world.xmlworld.xml

//country[name="Israel" or name="Spain"]/population

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<countries>


<name>Israel</name>




</country>


<name>France</name>


</country>

</countries>

world.xmlworld.xml//country/city[2]

• A number acts as an index

• That is, the number n evaluates to true if n is the position of the node among all those reached in the last step (i.e., city)

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FunctionsFunctions

• Inside XPath predicates, you can use a set of predefined functions

• Here are some examples:- last() – returns the number of nodes obtained from

the last axis step- position() – returns the position of the node in the list

of nodes satisfying the last axis step- name() – returns the name (tag) of the current node- count(XPath) – returns the number of nodes

satisfying XPath

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<countries>


<name>Israel</name>




</country>


<name>France</name>


</country>

</countries>

world.xmlworld.xml//country/city[last()]

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<countries>


<name>Israel</name>




</country>


<name>France</name>


</country>

</countries>

world.xmlworld.xml//city[position()<2]

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<countries>


<name>Israel</name>




</country>


<name>France</name>


</country>

</countries>

world.xmlworld.xml//*[name()="city" or name()="country"]

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<countries>


<name>Israel</name>




</country>


<name>France</name>


</country>

</countries>

world.xmlworld.xml//*[starts-with(name(),“c")]

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<countries>


<name>Israel</name>




</country>


<name>France</name>


</country>

</countries>

world.xmlworld.xml//country[count(./city)>=1]

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Final RemarksFinal Remarks

• The syntax of XPath that was presented here is the abbreviated syntax

• For example, city/../@name is an abbrv. of

child::city/parent::node()

/attribute::name

• More details on XPath:- XPath tutorial in W3Schools- XPath W3C Recommendation

http://www.w3schools.com/xpath/default.asp

http://www.w3schools.com/xpath/default.asp

http://www.w3.org/TR/xpath

http://www.w3.org/TR/xpath

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XSL Transformations XSL Transformations (XSLT)(XSLT)

An Example:

Useful Links in the DBI site

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XSLTXSLT

• XSLT is a language for transforming XML documents into other XML documents- For example, XHTML, WML- Can also transform XML to general text documents, e.g.,

SQL programs

• An XSLT program is itself an XML document (called an XSL stylesheet) that describes the transformation process for input documents

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Text

WML

DTD

XSLT ProcessorsXSLT Processors

XML

XSL

XSLT Processor

XHTML

44Web Page

Presentation

Doc. Structure

Data

Web Pages Web Pages –– The Whole Picture The Whole Picture

XMLXML

XSLXSL

XHTMLXHTML

Style

KnowledgeKnowledge

CSSCSS

DynamicsJavaScriptJavaScript

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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>

catalog.xmlcatalog.xml

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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>

Valid XML! Commands are XML elements with the namespace xslIncludes XHTML

elements

catalog.xslcatalog.xsl

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Applying XSL Stylesheets to XMLApplying 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, not the original XML

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Processing XSL in JavaProcessing XSL in Java

You can use the XALAN package of Apache in order to process XSL transformations

java org.apache.xalan.xslt.Process -IN myXmlFile.xml -XSL myXslFile.xsl -OUT myOutputFile.html

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How Does XSLT Work?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 to recursively process other nodes, e.g., the children of the current node

• Finally, the XSLT processor simply processes the root node of the document (that matches /)

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TemplatesTemplates

• 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 syntax for the pattern is a subset of XPath

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<html>



</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

view catalog1.xm

l

http://127.0.0.1:8080/dbi-examples/catalog.xml

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The ResultThe 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 catalog!</h1>

</body>

</html>

Implicitly added to <head>

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Examples of Match AttributesExamples 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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• Processing starts by applying a temp. to the root - If no specified template matches the root, then one is

inserted by default (see the next slide)

• You must specify explicitly whether templates should be applied to descendants of a node

• Done using the instruction:<xsl:apply-templates select="xpath"/>

- In xpath, cur. processed node is the context node

• Without the select attribute, this instruction processes all the children of the current node (including text nodes)

<xsl:apply-templates><xsl:apply-templates>

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Default TemplatesDefault Templates

• XSL provides implicit built-in templates that match every element and text nodes

• Templates we write always override these built-in templates (when they match)

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

</xsl:template>

<xsl:template match="text()|@*"><xsl:value-of select="."/>

</xsl:template>

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</xsl:stylesheet>

Dark Side of the Moon

Pink Floyd

10.90

Space Oddity

David Bowie

9.90

…

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<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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<h2>A cd!</h2>

<h2>A cd!</h2>

Aretha: Lady Soul

Aretha Franklin

9.90




<xsl:template match="cd[@country='UK']">

<h2>A cd!</h2></xsl:template>

</xsl:stylesheet>

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<h2>An artist!</h2>

<h2>An artist!</h2>




<xsl:apply-templates

select="catalog/cd[@country='UK']/artist"/>

</xsl:template>

<xsl:template match="artist">

<h2>An artist!</h2>

</xsl:template>

</xsl:stylesheet>

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<xsl:apply-templates

select="cd[@country='UK']/artist"/>

</xsl:template>

<xsl:template match="artist">

<h2>An artist!</h2>

</xsl:template>

</xsl:stylesheet>

Why?

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Frequently Used Elements of XSLFrequently Used Elements of XSL

• <xsl:value-of select="xpath"/>- This element extracts the value of a node from the

nodelist 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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<html><head><title>cd catalog</title></head>

<body>

<h1>CD catalog</h1>

<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>

Currently selected element is the context node

Example 1

catalog2.xsl

view catalog2.xm

l


64






<body>

<h1>CD catalog</h1>

<ul>


<li><xsl:apply-templates select="."/></li>

</xsl:for-each>

</ul></body></html>

</xsl:template>

Example 2

catalog3.xsl


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<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>

Example 2 (cont.)

Entities replace characters

price>10 → price<10

catalog3.xsl

view catalog3.xm

l


66

Example 3

<xsl:choose>:

Switch syntax for conditions

<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 The <xsl:sort><xsl:sort> Element 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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<body>

<h1>CD catalog</h1>

<ul>


<xsl:sort select="title"/>

<li><xsl:value-of select="title"/></li>

</xsl:for-each>

</ul></body></html>

</xsl:template>

</xsl:stylesheet>

CDs are iterated in ascending order of the titles

catalog4.xsl

view catalog4.xm

l

69

Setting Values in AttributesSetting Values in Attributes

• The <xsl:value-of> element cannot be used within an 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 ExampleAn Example

• In the following example, we add to each CD entitled t a link to the URL /showcd.php?title=t



<a href="/showcd.php?title={./title}">


</a>

</xsl:template>

view catalog5.xm

l

71

UsingUsing <xsl:element> <xsl:element>



<xsl:element name="a">

<xsl:attribute name="href">

showcd/?title=<xsl:value-of select="title"/>

</xsl:attribute>


</xsl:element>

</xsl:template>

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On XSL CodeOn 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 TemplatesOn 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> </xsl:template>

</xsl:stylesheet>

Identity TransformationStylesheet

75

Generating Valid XHTMLGenerating 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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<html>



</html>

</xsl:template>

</xsl:stylesheet>

The Original XSL ExampleThe Original XSL Example

77

<html>

<head>

<META http-equiv="Content-Type" content="text/html; charset=UTF-8">


</head>

<body>


</body>

</html>

Uppercase tag name, unclosed element

No DOCTYPE

The Original Transformation ResultThe Original Transformation Result

78



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="/"> …

Modifying the XSL ExampleModifying the XSL Example

79

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">

<head>


</head>

<body>


</body>

</html>

META is not inserted

The Transformation ResultThe Transformation Result

80

Some Other XSL ElementsSome 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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Costello’s TutorialCostello’s Tutorial

Costello has an excellent, detailed tutorial- First part (xsl01.ppt) has many examples that do

not use recursion- Second part (xsl02.ppt) explains how to use

recursion and why it is needed (the identity

transformation shown earlier is from Costello’s

tutorial)

(See DBI timetable for a reference)

82

W3Schools Tutorial on XSLTW3Schools 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

http://www.w3schools.com/xsl/default.asp

extensible stylesheet language (xsl)

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