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CSE3201/CSE4500

XPath

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XPath

• A locator for elements or attributes in an XML document.

• XPath expression gives direction of navigation to the parser.

• Assume an XML document as a “tree”• Any part of a document, eg element, attribute, is

considered as a “node”• Current version XPATH 1.0

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XPath

• Syntax (full form):axis :: node-test [predicate]

• Axis– describing the relationship between nodes, eg child,

parents, etc.• Node test

– condition for selecting nodes.• Predicate:

– further condition refinement of the set of nodes resulted from the node test.

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XPath Axes

Ancestor

Parent/ancestor

sibling

node

child/descendant

descendantattribute

sibling

context node

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Node Test

• A node test identifies nodes in the document that meet the criteria of the test.

• The simplest type of test is nodes that match an element name.

• Example:

child::book => to find any child element with the name “book”.

child::author

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Predicate

• Predicate further refine or filter the node-set produced by the node test.

• Example:– Find the third book in the list

> child::book[position( )=3]

– Find all the books that has <isbn> element> child::book[isbn]

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Abbreviations

Formal Short Description

child::book book Select all children of the context node that has <book> element nodes.

child::* * Select all element nodes of the context node.

self::node() . Select the context node.

parent::node() .. Select the parent of the context node.

child::book[position()=1]

book[1] Select the first child element that has <book> element.

attribute::* @* select all the attributes of the context node

attribute::number @number Find the number of attributes in the context node.

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Location Path

Document Root

<name>

<first>

<middle>

“John”

“Little”

<last>

“Howard”

/name/first

Uses “/” to build path, eg

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Relative vs Absolute Path

• Absolute Path– full path needs to be included, starting from the

root node.> eg: /name/first

• Relative Path– path is declared starting from the current context

node.> eg: assume our current context is “name”, the XPath

expression for the node first => first

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Recursive Decent Operator

• Locating nodes based on their names, regardless of where their positions in the document.

• Uses “//”• Example: //first

– Select any <first> element in the document (regardless how far down the tree).

• Decrease the performance of the stylesheet.– The entire document must be searched by the XSLT

parser.

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Filtering Nodes

• It is done using XPath’s predicate.– the “[ ]” symbol.

• Using element as a filter: – book[price] matches any <book> element that

has a <price> child element.• Using attribute as a filter:

– book[@id] matches any <book> element that has an id attribute.

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XPath Expression

• Some possible operators to build an XPath Expression:

and Logical AND

or Logical OR

not() logical negation

= Equal

!= Not equal

< Less than

<= Less than equal

> Greater than

>= Greater than equal

| Union

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XPath Expression - Examples

• <xsl:template match="/">• <xsl:if test=“not(position()=last())”>

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XPath Function

• XPath functions can be used to:– manipulate node set

> eg: count, last, name, position

– manipulate string> eg: concat, substring, contains

– test boolean value> eg: language, false, true

– perform numeric operations> eg: ceiling, floor, number, round, sum

– XSLT specific manipulation> eg: current

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XPath Function - Examples

• <xsl:if test=“not(position()=last())”>• substring(‘abcde’,2,3) => returns ‘bcd’

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CSE3201/CSE4500 Information Retrieval Systems

XSLT

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Manipulating XML Documents

parser

data

data

data

Applications

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What is XSL

• Extensible Stylesheet Language• Developed by W3C XSL Working Group• Motivation: to handle the manipulation and

presentation of XML documents• Consists of: XSLT and XSL-FO

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XSL

Stylesheet processor

XML document

XSL document

Presentation document

Transformation process

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Transformation Tools

• XPath• XSL(Extensible Stylesheet Languages)

– XSLT(XSL Transformation)– XSL-FO(XSL Formatting Object)

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Transformation Process

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XSLT Processing

• Type of processings:– Change of vocabulary– Reorder data elements– Combine data elements– Filter and exclude data elements

• Output– Other XML vocabularies or fragments– Non-XML formats

• Uses– Display and printing– Transformation of data

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Example of a Stylesheet

<?xml version="1.0"?>

<!-- Query: List the surname of all author-->

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">

<xsl:output method="html"/>

<xsl:template match="/">

<html>

<body>

<h1>Monash Bookshop</h1>

<h2>Authors Surname</h2>

<xsl:apply-templates select="bookshop/book"/>

</body>

</html>

</xsl:template>

<xsl:template match="bookshop/book">

<xsl:apply-templates select="author"/>

</xsl:template>

<xsl:template match="author">

<xsl:apply-templates select="surname"/>

</xsl:template>

<xsl:template match="surname">

<p>

<xsl:value-of select="."/>

</p>

</xsl:template>

</xsl:stylesheet>

<bookshop><book><title> Harry Potter and the Sorcerer stone </title><author> <initials>J.K</initials> <surname> Rowling</surname></author><price value=“$16.95”></price></book>…</bookshop>

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Usage of XPath in XSLT

• XSLT uses XPath expression to:– Match node sets in order to execute templates.

> <xsl:template match=“/">

– Select node sets to change current context and direct the flow of the execution through the source document.

> <xsl:apply-templates select = bookshop/book/>

– Select node sets to obtain an output value> <xsl:value-of select=“."/>

Professional XML, page 379.

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Structure of Stylesheet

• An XSLT stylesheet is an XML document.• Root element is stylesheet element

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">

…

</xsl:stylesheet>

• Consists of a set of rules.• Rules are made up of patterns and templates.

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Attaching an XSL to an XML doc

<?xml-stylesheet type="text/xsl" href="books.xsl"?>

• href refers to the filename of the XSL document.

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Selecting Output Type

• Possible outputs:– XML, HTML, Text

• Syntax:<xsl-output method=“xml”/>

<xsl-output method=“text”/>

<xsl-output method=“html”/>

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Templates

• To create a template, we need:– To declare the location in the source tree where

the template will be applied.– Rules of matching to be applied.

> can be another template

• The location is declared using the XPath expression.

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Using Templates

• Templates are executed when the condition in the <xsl:apply template> are met.

• <xsl:apply-templates  select = node-set-expression> </xsl:apply-templates>

• The “select” attribute is optional.• Without the “select” attribute, the XSL

processor will apply the templates to all the child elements of the current context node.

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Template Examples

<?xml version="1.0"?><xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"

version="1.0"><xsl:output method="html"/><xsl:template match="/"> <html> <body> <h1>Book</h1> <xsl:apply-templates/> </body> </html></xsl:template></xsl:stylesheet>

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Selecting Templates

<?xml version="1.0"?><xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"

version="1.0">

<xsl:output method="html"/>

<xsl:template match="/"> <html> <body> <h1>Monash Bookshop</h1> <xsl:apply-templates select="bookshop/book"/> </body> </html></xsl:template>

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Selecting Templates- cont’d

<xsl:template match=“bookshop/book" >

<xsl:apply-templates select="author"/>

<xsl:value-of select="@type"/>

</xsl:template>

<xsl:template match="author">

<h2>Author</h2>

<xsl:value-of select="."/>

</xsl:template>

</xsl:stylesheet>

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Getting the Value of a Node

xsl:value-of select=XPath expression

Examples:Element

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

Attribute

<xsl:value-of select=“@type”>

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Iteration

• Combination of template and apply-templates

• <xsl:for-each>• Compared the iteration.xsl and iterationTemplate.xsl

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Conditional Test

• IF statement is used to change the tree traversing process.– Process a node differently from the rest of the nodes in the same family.– Eg. Print bold only for the first item in the list.

• xsl:if– there is no “else” statement.– takes one attribute, test, which is an XPath expression. – if it evaluates true, the body of the element is executed

• xs:choice– Test for multiple conditions

• Good practises:– Do NOT use the IF statement to select a node in a tree, use the XPATH to do that.

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Conditional Test - Example

• Example:

Give yellow colour to alternate rows <xsl:template match=“customers/customer">

<tr>

<xsl:if test="position() mod 2 = 0">

<xsl:attribute name="bgcolor">yellow</xsl:attribute>

</xsl:if>

<th>

<xsl:apply-templates select="name"/>

</th>

<xsl:apply-templates select="order"/>

</tr>

</xsl:template>

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Conditional Test - Note

XPath

<xsl:apply-template select=“customers/customer[name=‘Maria’/>

<xsl:template match=“customers/customer”>

<xsl:value-of select=“name”/>

</xsl:template>

xsl:if

<xsl:apply-template select=“customers/customer”/>

<xsl:template match=“customers/customer”><xsl:if test=“name=‘Maria’”>

<xsl:value-of select=“name”></xsl:if>

</xsl:template>

•Avoid using conditional test xsl:if to match a node. Use the XPath expression instead.

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Making Copies

• xsl:copy

– It does not copy any child nodes that the context node may have.• xsl:copy-of

– copies all

<xsl:template match="/bookshop"> <html> <body> <h1>Book</h1> <xsl:copy/> </body> </html></xsl:template>

<html><body><h1>Book</h1><bookshop></bookshop> </body> </html>

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Copy-of

<?xml version="1.0" encoding="utf-8"?><Author_List> <author>

<initials>JK</initials><surname> Rowling</surname>

</author> <author>

<initials>J</initials><surname> Rowling</surname>

</author></Author_List>

<?xml version="1.0"?><xsl:stylesheet version = '1.0' xmlns:xsl='http://www.w3.org/1999/XSL/Transform'><xsl:output method="xml"/>

<xsl:template match="/"><xsl:element name="Author_List"><xsl:apply-templates/></xsl:element></xsl:template>

<xsl:template match="bookshop/book"><xsl:copy-of select="author"/></xsl:template>

</xsl:stylesheet>