XPATH
Modified Slides from
Dr. Sagiv
1
XPath
• A Language for Locating Nodes in XML Documents
• XPath expressions are written in a syntax that
resembles paths in file systems
• The list of nodes located by an XPath expression is
called a Nodelist
• XPath is used in XSL and in XQuery (a query language
for XML)
• W3Schools has an XPath tutorial
• XPath includes
– Axis navigation
– Conditions
– Functions
2
<?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>
An XML document
</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>
3
</catalog>
catalog.xml
catalog
country
UK
cd
country
title artist price
UK
cd
cd
Pink Floyd
10.90
USA
title artist price title artist price
Space Oddity
Dark Side of
the Moon
country
Aretha: Lady
Soul
David Bowie
9.90
Aretha Franklin
9.90
4
The Main Idea in the Syntax of
XPath Expressoins
• “/” at the beginning of an XPath expression
represents the root of the document
• “/” between element names represents a
parent-child relationship
• “//” represents an ancestor-descendent
relationship
• “@” marks an attribute
• “[condition]” specifies a condition
5
catalog.xml
catalog
cd
country
UK
country
title artist price
UK
/catalog
cd
cd
USA
title artist price title artist price
Space Oddity
Dark Side of
the Moon
Pink Floyd
10.90
country
Aretha: Lady
Soul
David Bowie
Aretha Franklin
9.90
Getting the root element of the document
9.90
6
catalog.xml
catalog
country
UK
cd
country
title artist price
UK
/catalog/cd
cd
cd
USA
title artist price title artist price
Space Oddity
Dark Side of
the Moon
Pink Floyd
10.90
country
Aretha: Lady
Soul
David Bowie
9.90
Finding child nodes
Aretha Franklin
9.90
7
catalog.xml
catalog
country
UK
cd
country
title artist price
UK
/catalog/cd/price
cd
cd
USA
title artist price title artist price
Space Oddity
Dark Side of
the Moon
Aretha: Lady
Soul
David Bowie
Pink Floyd
10.90
country
Aretha Franklin
9.90
Finding descendent nodes
9.90
8
catalog.xml
catalog
country
UK
cd
country
title artist price
UK
/catalog/cd[price<10]
cd
cd
USA
title artist price title artist price
Space Oddity
Dark Side of
the Moon
Aretha: Lady
Soul
David Bowie
Pink Floyd
10.90
country
Aretha Franklin
9.90
Condition on elements
9.90
9
catalog.xml
country
UK
cd
country
title artist price
UK
catalog
//title
cd
cd
Pink Floyd
10.90
country
USA
title artist price title artist price
Space Oddity
Dark Side of
the Moon
/catalog//title
Aretha: Lady
Soul
David Bowie
Aretha Franklin
9.90
// represents any directed path in the document
9.90
10
catalog.xml
catalog
country
UK
cd
country
title artist price
UK
/catalog/cd/*
cd
cd
USA
title artist price title artist price
Space Oddity
Dark Side of
the Moon
Pink Floyd
10.90
country
Aretha: Lady
Soul
David Bowie
Aretha Franklin
9.90
* represents any element name in the document
9.90
11
catalog.xml
What will the following
expressions return?
country
UK
cd
catalog
country
title artist price
UK
cd
cd
USA
title artist price title artist price
Space Oddity
Dark Side of
the Moon
Pink Floyd
10.90
country
Aretha: Lady
Soul
David Bowie
Aretha Franklin
9.90
* represents any element name in the document
9.90
12
catalog.xml
/catalog/cd[1]
catalog
country
UK
cd
country
title artist price
UK
/catalog/cd[last()]
cd
cd
USA
title artist price title artist price
Space Oddity
Dark Side of
the Moon
Aretha: Lady
Soul
David Bowie
Pink Floyd
10.90
country
Aretha Franklin
9.90
Position based condition
9.90
13
catalog.xml
/catalog/cd[@country=“UK”]
catalog
country
UK
cd
country
title artist price
UK
cd
cd
USA
title artist price title artist price
Space Oddity
Dark Side of
the Moon
Pink Floyd
10.90
country
Aretha: Lady
Soul
David Bowie
9.90
@ marks attributes
Aretha Franklin
9.90
14
catalog.xml
catalog
/catalog/cd/@country
country
UK
cd
country
title artist price
UK
cd
cd
USA
title artist price title artist price
Space Oddity
Dark Side of
the Moon
Pink Floyd
10.90
country
Aretha: Lady
Soul
David Bowie
9.90
@ marks attributes
Aretha Franklin
9.90
15
Relative Navigation Using Axes
• Starts with the current node and not with
the root (/)
• A . marks the current node (e.g., ./title)
• A .. marks the parent node (e.g., title/../*)
• There are also other axes, e.g., child,
descendent, ancestor, parent, followingsibling, etc.
16
Functions
• Many functions that are included in XPath
• Some examples:
– count() – returns the number of nodes in a
nodelist
– last() – returns the last node in a nodelist
– name() – returns the name of a node
– position() – returns the position of the node in
the nodelist
17
Additional Examples of
XPath Expressions
These examples use element names
that are not necessarily from the XML
document that was shown previously
18
Examples of XPath Expressions
• para
– Selects the para children elements of the context
node
• *
– Selects all element children of the context node
• text()
– Selects all text node children of the context node
• @name
– Selects the name attribute of the context node
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More Examples of
XPath Expressions
• @*
– Selects all the attributes of the context node
• para[1]
– Selects the first para child of the context node
• para[last()]
– Selects the last para child of the context node
• */para
– Selects all para grandchilren of the context node
20
More Examples of
XPath Expressions
• /doc/chapter[5]/section[2]
– Selects the second section of the fifth chapter of the
doc
• chapter//para
– Selects the para element descendants of the chapter
element children of the context node
• //para
– Selects all the para descendants of the document
root and thus selects all para elements in the same
document as the context node
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More Examples of
XPath Expressions
• //olist/item
– Selects all the item elements that have an olist
parent and are in the same document as the context
node
• .
– Selects the context node
• .//para
– Selects the para descendants of the context node
• ..
– Selects the parent of the context node
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More Examples of
XPath Expressions
• ../@lang
– Selects the lang attribute of the parent of the
context node
• para[@type=“warning”]
– Selects the para children of the context node
that have a type attribute with value warning
• chapter[title]
– Selects the chapter children of the context
node that have one or more title children
23
More Examples of
XPath Expressions
• para[@type=“warning”][5]
– Selects the fifth para child among the
children of the context node that have a type
attribute with value warning
• para[5][@type=“warning”]
– Selects the fifth para child of the context
node if that child has a type attribute with
value warning
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More Examples of
XPath Expressions
• chapter[title=“Introduction”]
– Selects the chapter children of the context
node that have one or more title children with
string-value equal to Introduction
• employee[@secretary and @assistant]
– Selects employee children of the context
node that have both a secretary attribute and
an assistant attribute
25
More Examples of
Xpath Expressions
• /university/department/course
– This Xpath expression matches any path that
starts at the root, which is a university
element, passes through a department
element and ends in a course element
• ./department/course[@year=2002]
– This Xpath expression matches any path that
starts at the current element, continues to a
child which is a department element and
ends at a course element with a year
attribute that is equal to 2002
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Location Paths
• The previous examples are abbreviations
of location paths
– See XPath tutorial in W3Schools
– For example, // is short for
/descendant-or-self::node()/.
• //para is short for
/descendant-or-self::node()/child::para
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