1 xpath 1.0 roger l. costello 6 march 2010

XPath 1.0

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

Roger L. Costello6 March 2010

XPath is not a standalone language

XQuery

XMLSchemas

XPointer

Schematron

A complete list of technologies that use XPath:http://expath.org/wiki/Engines

Document/

PI<?xml version=“1.0”?>

ElementFitnessCenter

ElementMember

ElementName

ElementFavoriteColor

TextJeff

Textlightgrey

ElementName

TextDavid

Textlightblue

ElementName

TextRoger

Textlightyellow

<?xml version="1.0"?><FitnessCenter> <Member> <Name>Jeff</Name> <FavoriteColor>lightgrey</FavoriteColor> </Member> <Member> <Name>David</Name> <FavoriteColor>lightblue</FavoriteColor> </Member> <Member> <Name>Roger</Name> <FavoriteColor>lightyellow</FavoriteColor> </Member></FitnessCenter>

This XML document can berepresented as a tree, as shown below

Terminology: node

Document/

ElementMember

ElementName

TextJeff

Textlightgrey

ElementName

TextDavid

Textlightblue

ElementName

TextRoger

Textlightyellow

Document nodeProcessing Instruction (PI) node

Element nodes

Text nodes

Document/

ElementMember

ElementName

TextJeff

Textlightgrey

ElementName

TextDavid

Textlightblue

ElementName

TextRoger

Textlightyellow

With respect to this node, these are its children

Document/

ElementMember

ElementName

TextJeff

Textlightgrey

ElementName

TextDavid

Textlightblue

ElementName

TextRoger

Textlightyellow

These are its descendant nodes

Document/

ElementMember

ElementName

TextJeff

Textlightgrey

ElementName

TextDavid

Textlightblue

ElementName

TextRoger

Textlightyellow

This is the context node

Document/

ElementMember

ElementName

TextJeff

Textlightgrey

ElementName

TextDavid

Textlightblue

ElementName

TextRoger

Textlightyellow

That's its parent

Document/

ElementMember

ElementName

TextJeff

Textlightgrey

ElementName

TextDavid

Textlightblue

ElementName

TextRoger

Textlightyellow

Those are its ancestors

Document/

ElementMember

ElementName

TextJeff

Textlightgrey

ElementName

TextDavid

Textlightblue

ElementName

TextRoger

Textlightyellow

It has 2 siblings

Document/

ElementMember

ElementName

TextJeff

Textlightgrey

ElementName

TextDavid

Textlightblue

ElementName

TextRoger

Textlightyellow

They are following-siblings

Document/

ElementMember

ElementName

TextJeff

Textlightgrey

ElementName

TextDavid

Textlightblue

ElementName

TextRoger

Textlightyellow

It has no preceding-siblings

Here are the capabilities of XPath

• XPath provides a syntax for: – navigating around an XML document– selecting nodes and values – comparing node values– performing arithmetic on node values

• XPath provides some functions (e.g., concat(), substring()) to facilitate the above.

Document/

ElementDocument

ElementPara

TextOne if …

TextAnd I …

TextReady to

<?xml version="1.0"?><Document classification="secret"> <Para classification="unclassified"> One if by land, two if by sea; </Para> <Para classification="confidential"> And I on the opposite shore will be, Ready to ride and spread the alarm </Para> <Para classification="unclassified"> Ready to ride and spread the alarm Through every Middlesex, village and farm, </Para></Document>

This XML document can berepresented as a tree, as shown below

Attributeclassification=“secret”

Attributeclassification=“unclassified”

Attributeclassification=“confidential”

Execute XPath using Oxygen XML

Type your XPath expression here

Change this to XPath 1.0

Use XPath Builderfor long XPathexpressions

Please Execute the XPath Expressions

• The following slides contain XPath expressions.

• It is important that you copy the expression on the slide and paste it into Oxygen XML to see what the expression does.

• Now, drag and drop Document.xml (in the example000 folder) into Oxygen XML.

Select all Para Elements

/Document/Para

Document/

ElementDocument

ElementPara

TextOne if …

TextAnd I …

TextReady to

/Document/Para

“Hey XPath processor, position yourself at the Document node (i.e., /); use that as the ‘context node’; from there select any child elements with the name ‘Document’ (there’s only one); now use that as the context node and from there select any child elements with the name Para (there are four, although only three are shown below due to space limitations). Show the selected set of nodes.”

Result

<Para classification="unclassified"> One if by land, two if by sea;</Para><Para classification="confidential"> And I on the opposite shore will be, Ready to ride and spread the alarm</Para><Para classification="unclassified"> Ready to ride and spread the alarm Through every Middlesex, village and farm,</Para><Para classification="secret"> For the country folk to be up and to arm.</Para>

Evaluating the XPath query results in selecting each Para element, including its attribute and contents.

Here’s how Oxygen displays the results

Please understand what this is saying: the first Para element (Para[1]) and its content is selected, the second Para element and its content is selected, the third Para and its content is selected, and the fourth Para element and its content is selected.

/Document/Para

This is an absolute XPath expression. i.e., the selection of nodes starts from the top of the document (tree).

Absolute XPath Expression

Not XML!

• XPath syntax is not XML syntax!

Establish a Context Node

Click on this to establish Document as the "context node"(this will allow you to create XPath expressions that are relative to it)

Relative XPath Expression

In Oxygen XML click on <Document> toestablish the context node and then typethis in the XPath box:

Result

Same result as before.

Select “here”

In Oxygen XML click on <Document> toestablish the context node and then typethis in the XPath box:

Result<Document classification="secret"> <Para classification="unclassified"> One if by land, two if by sea; </Para> <Para classification="confidential"> And I on the opposite shore will be, Ready to ride and spread the alarm </Para> <Para classification="unclassified"> Ready to ride and spread the alarm Through every Middlesex, village and farm, </Para> <Para classification="secret"> For the country folk to be up and to arm. </Para></Document>

The context node is selected, which is Document. Thus the result is Document and its content.

Select all Para Descendents

//Para

The double slash means “descendents.”

Result

All Para elements that descend from / are selected.

Select the first Para

//Para[1]

Result

The first Para element is selected.

Select the last Para

//Para[last()]

Result

<Para classification="secret"> For the country folk to be up and to arm.</Para>

last() is an XPath function. It returns a number (in our example it returns 4). Thus the fourth (last) Para element is selected.

Select the classification attribute of the first Para

//Para[1]/@classification

Result

unclassified

The @ symbol means “attribute.” Thus, the value of the classification attribute, of the first Para element, is selected.

Is the Document element’s classification top-secret?

/Document/@classification = 'top-secret'

The XPath expression uses the equality comparison operator.

Result

=<>!=<=>=

Comparison Operators

Remember to escape the reserved characters: Instead of < use <

Instead of > use >Instead of <= use <=Instead of >= use >=

Is the Document element’s classification top-secret or

secret?

(/Document/@classification = 'top-secret') or (/Document/@classification='secret')

The XPath expression uses the boolean “or” operator.

Result

A or BA and Bnot(A)

Boolean Operators

Select all Para’s with a secret classification

//Para[@classification = 'secret']

Result

<Para classification="secret"> For the country folk to be up and to arm.</Para>

Check that no Para has a top-secret classification

not(//Para[@classification = 'top-secret'])

Result

Select the Para’s that don’t have a top-secret classification

//Para[@classification != 'top-secret']

Result

None of the Para elements have a top-secret classification.Do Lab1

Establish a New Context Node

Make the second Para the context node

Select the Following Siblings

following-sibling::*

Result

<Para classification="unclassified"> Ready to ride and spread the alarm Through every Middlesex, village and farm,</Para><Para classification="secret"> For the country folk to be up and to arm.</Para>

These Para elements are siblings (of the second Para element) and they follow, i.e., they are following siblings.

Select the FirstFollowing Sibling

following-sibling::*[1]

Result

<Para classification="unclassified"> Ready to ride and spread the alarm Through every Middlesex, village and farm,</Para>

Add Another Element

Add this <Test> element after the last Para

Set the Context Node

Make the second Para the context node

Select the Following Para Siblings

following-sibling::Para

Result

<Para classification="unclassified"> Ready to ride and spread the alarm Through every Middlesex, village and farm,</Para><Para classification="secret"> For the country folk to be up and to arm.</Para>

Although the Test element is a following sibling of Para[2], it is not selected because the XPath expression selects only the Para following siblings.

Select all Following Siblings

following-sibling::*

Result

<Para classification="unclassified"> Ready to ride and spread the alarm Through every Middlesex, village and farm,</Para><Para classification="secret"> For the country folk to be up and to arm.</Para><Test>Hello World</Test>

The * symbol matches (selects) any element node.

Select the First Following Para Sibling

following-sibling::Para[1]

Result

<Para classification="unclassified"> Ready to ride and spread the alarm Through every Middlesex, village and farm,</Para>

Select all Preceding Siblings

preceding-sibling::*

Result

Para[2] has only one preceding sibling element node.

Establish a New Context Node

Click on Document to make it thecontext node.

Equivalent!

Para[1]

child::Para[1]

The first XPath expression is called the abbreviated notation. The second XPath expression is called the long notation.

Make Para[2] the context

Establish this as the context node.

Get parent element's classification

../@classification

Means go up one level (to the parent).

Equivalent!

../@classification

parent::*/@classification

Recall x, y Axes from School

• The x, y axes enables us to navigate through space.

• Similarly, we want to navigate through an XML document. So we need some axes for navigating through XML documents.

• We need a much richer set of axes than the x, y axes. We need axes that enables us to navigate to child nodes, to all descendent nodes, to the parent node, to all ancestor nodes, etc.

List of Axis

• ancestor: use to select all ancestors

• ancestor-or-self: use to select the current node plus all its ancestors

• attribute: use to select attributes

• child: use to select child nodes

• descendant: use to select all the descendants

• descendant-or-self: use to select the current node plus all its descendants

• following: use to select everything in the document that follows the current node

• following-sibling: use to select the siblings that follow

• namespace: use to select the namespaces that are in scope

• parent: use to select the parent

• preceding: use to select everything in the document that precedes the current node

• preceding-sibling: use to select the siblings that precede

• self: use to select the current node

Load this XML Document into Oxygen

<?xml version="1.0"?><FitnessCenter> <Member level="platinum"> <Name>Jeff</Name> <Phone type="home">555-1234</Phone> <Phone type="work">555-4321</Phone> <FavoriteColor>lightgrey</FavoriteColor> </Member></FitnessCenter>

This is in the example000 folder, the file is FitnessCenter.xml

Document/

ElementMember

ElementName

ElementPhone

TextJeff

Text555-1234

Text555-4321

Textlightgrey

ancestors

precedingsibling

followingsiblings

If the context node is the Member's first phone element then: we can select all ancestors by: all preceding siblings by: all following siblings by: ancestor::* preceding-sibling::* following-sibling::* Which yields: Which yields: Which yields: Member Name Phone FitnessCenter FavoriteColor

Document/

ElementMember

ElementName

ElementPhone

TextJeff

Text555-1234

Text555-4321

Textlightgrey

descendants

If the context node is the FitnessCenter element then: we can select all descendants by: descendant::* Which yields: Member Name Phone, etc.

Using an Axis

axis::node

Either the name of an element or the * symbol

Examples: ancestor::* child::Para

Reload this Document

Let’s go back to this document.

Common Error

• Distinguish between these two:child::Parachild:Para

• The first one has two colons, the second has only one.

• When specifying an axis you must follow it with two colons. (Otherwise the XPath processor will think that you’re using a namespace!)

Default Axis

Para[1]

child::Para[1]

“child” is the default axis, i.e., if an XPath expression doesn’t specify an axis (see the first expression above) then, by default, the child axis is used.

Do Lab2

XPath Functions

• Thus far we have been creating XPath expressions that select nodes and compare nodes in the XML document.

• The following slides show XPath expressions that operate on nodes in the XML document. This is accomplished using XPath functions.

Count the number of Para elements

count(//Para)

Result: 4

Count the number of Para elements with secret

classification

count(//Para[@classification = 'secret'])

Result: 1

Add SCRIPT to the First Para

Add this word

Does the first Para element contain the string “SCRIPT”?

contains(//Para[1], 'SCRIPT')

Result: true

6 Kinds of Nodes

• An XML document contains these kinds of nodes:– Element nodes

– Attribute nodes

– Text nodes

– Document node

– Comment nodes

– Processing instruction nodes

• The node() function matches any kind of node.

node() vs *

• As we’ve seen, the * symbol matches (selects) element nodes.

• The node() function matches (selects) any kind of node.

Select all nodes containing the string “SCRIPT”

//node()[contains(., 'SCRIPT')]

For each node in the XML document: If it contains SCRIPT then select (output) it.

Document/

ElementDocument

ElementPara

TextOne if …SCRIPT

TextAnd I …

TextReady to

This element node contains SCRIPT

This text node contains SCRIPT

This element node contains SCRIPT

Result<Document classification="secret"> <Para classification="unclassified"> One if by land, two if by sea;SCRIPT </Para> <Para classification="confidential"> And I on the opposite shore will be, Ready to ride and spread the alarm </Para> <Para classification="unclassified"> Ready to ride and spread the alarm Through every Middlesex, village and farm, </Para> <Para classification="secret"> For the country folk to be up and to arm. </Para></Document><Para classification="unclassified"> One if by land, two if by sea;SCRIPT</Para>One if by land, two if by sea;SCRIPT

Count the number of nodes containing the string “SCRIPT”

count(//node()[contains(., 'SCRIPT')])

Result: 3

Select the first 20 characters of the first Para

substring(//Para[1], 1, 20)

Result: cr One if by

carriage return

10 spaces

substring(string, num1, num2?)

• The first two arguments of the substring function are mandatory. The third argument is optional.

• If the third argument is omitted then the function will return all the characters from num1 to the end of the string.

substring(//Para[1], 10) returns all characters from character 10 onward

What's the length of the content of the first Para?

string-length(//Para[1])

Result: 52

What's the name of the last child element of Document?

name(/Document/*[last()])

Result: Test

translate(/Document/@classification, 'abcdefghijklmnopqrstuvwxyz', 'ABCDEFGHIJKLMNOPQRSTUVWXYZ')

Convert Document’s classification to uppercase

Result: SECRET

translate(string, from pattern, to pattern)

• The translate function has three arguments:– A value to be translated– A set of characters to convert from– A set of characters to convert to

• Each character in string is examined. If that character is in from pattern then it is changed to the character at the same position in to pattern. If that character is not in from pattern then it is output unchanged.

Add a new <Cost> element

Add this element and establishDocument as the context node.

Multiply Cost by 2

Cost * 2

Result: 24

N mod X = the remainder of dividing N by X

Cost mod 2

Result: 0

Arithmetic Operators

*mod- (must leave space on either side)+div

Do Lab3

Load this XML Documentinto Oxygen

<?xml version="1.0"?><FitnessCenter> <Member> <Name>Jeff</Name> <FavoriteColor>lightgrey</FavoriteColor> </Member> <Member> <Name>David</Name> <FavoriteColor>lightblue</FavoriteColor> </Member> <Member> <Name>Roger</Name> <FavoriteColor>lightyellow</FavoriteColor> </Member> <Employee> <Name>Erika</Name> </Employee> <Employee> <Name>Linda</Name> </Employee> <CEO> <Name>Jack</Name> </CEO> <VP> <Name>Dora</Name> </VP></FitnessCenter>

See FitnessCenter_v2.xml in the example000 folder.

Establish FitnessCenter as the Context Node

Click on this to make it the context node.

3 Forms of XPath Expressions

• Path Expression: expression1/expression2– Example: Member/Name

• Predicate Expression: expression1[expression2]– Example: Member[Name]

• Union Expression: expression1|expression2– Example: Member/Name|Member/Age

– Note: the "|" operator computes the union of its operands, which must be node sequences.

Context Item

• Consider this path expression: Member/Name, and this predicate expression: Member[Name].

• In these expressions Name is evaluated once for each item in the sequence that results from evaluating Member.

<Member> <Name>Jeff</Name> <FavoriteColor>lightgrey</FavoriteColor></Member><Member> <Name>David</Name> <FavoriteColor>lightblue</FavoriteColor></Member><Member> <Name>Roger</Name> <FavoriteColor>lightyellow</FavoriteColor></Member>

Context Item

• Evaluating the expression "Member" produces this sequence of element nodes:

<Member> <Name>Jeff</Name> <FavoriteColor>lightgrey</FavoriteColor></Member>

<Member> <Name>David</Name> <FavoriteColor>lightblue</FavoriteColor></Member>

<Member> <Name>Roger</Name> <FavoriteColor>lightyellow</FavoriteColor></Member>, ,

"Name" is evaluated once for eachitem in this sequence. Each of theseMember nodes is the context itemfor evaluating Name.

Defn: The context item is the item (node) that provides the context for evaluating an inner expression.

Meaning of "/"

• Consider this path expression: Member/Name

• The "/" means: "for each Member node, return the result of evaluating Name".

Member/Name <Name>Jeff</Name>

<Name>David</Name>

<Name>Roger</Name>

Meaning of "/" (concluded)

• Here is the general form for using "/"expression1/expression2

Each of these expressions must evaluate toa node, or sequence of nodes.Consequently, this is illegal:

Member/last()

This evaluates to an integer, not a node.

Meaning of […]

• Consider this predicate expression: Member[Name]• The predicate [Name] means: evaluate the expression "Name"

within the context node. If Name exists then return true, else false.

• Thus, Member[Name] says: "give me all Member nodes that has a Name child".

Member[Name]

<Member> <Name>David/Name> <FavoriteColor>lighblue</FavoriteColor></Member>

<Member> <Name>Roger</Name> <FavoriteColor>lightyellow</FavoriteColor></Member>

Meaning of […] (concluded)

• Here is the general form for using […]expression1[expression2]

This expression must evaluate toa node or node sequence.

Consequently, all of these are legal: Member[true()]

Member[false()] Member[1 = 1]

Member[1 = 2]Member[Age]

This expression must evaluate toa boolean value (true or false).

These will select all Member elements

These will select no Member elements

This will select only the Member elements thathave an Age child element.

Meaning of "|"

• Consider this union expression: expression1|expression2

• The union expression means, "create a sequence of nodes composed of the nodes selected by expression1, unioned with the nodes selected by expression2.

<Member> <Name>Jeff</Name> <FavoriteColor>lightgrey</FavoriteColor></Member><Member> <FavoriteColor>lightblue</FavoriteColor></Member><Member> <Name>Roger</Name> <FavoriteColor>lightyellow</FavoriteColor></Member>

Member[1]|Member[3]

<Member> <Name>Roger</Name> <FavoriteColor>lightyellow</FavoriteColor></Member>

Context Position

• Recall that an XPath expression returns a sequence of items.

• Consider one of those items in the sequence. Its context position is the position of the item in the sequence.

The context position is returned by the function position()

Member[position() = 2] “Evaluate the expression: MemberIt yields a sequence of 3 Member nodes.Give me the one at position 2.”

Result:<Member> <Name>David/Name> <FavoriteColor>lighblue</FavoriteColor></Member>

Equivalent!

Member[position() = 2]

Member[2]

The latter is a shorthand for the former.

Context Size

• Recall that an expression returns a sequence of items.

• The context size tells you the number of items in the sequence.

The context size is returned by the expression last()

Member[last()] “Evaluate the expression: MemberIt yields a sequence of Member nodes.Give me the last one.”

Result:<Member> <Name>Roger</Name> <FavoriteColor>lightyellow</FavoriteColor></Member>

• There are many ways that you might want to navigate through an XML tree. For example, from a context node you might want to: – navigate to a child node – navigate to an ancestor node– navigate to a preceding sibling node– navigate to a descendant node, etc.

• An axis is provided for each way that you might want to navigate through an XML tree.

• The syntax for using an axis is: axis::node

Categories of Axes• These are axes used for navigating forward in the XML

tree:– child– descendant– attribute– self– descendant-or-self– following-sibling– following

• These are axes used for navigating backward in the XML tree:

– parent– preceding-sibling– preceding– ancestor– ancestor-or-self

Child Axis

• The child axis is used to navigate to a child node from the context node.

./child::Member[1]/child::Name

Starting from the context node, navigate toa child node - the first Member. Now, usingthat Member as the context node, navigateto a child node - the Name node.

Document/

ElementMember

ElementName

TextJeff

Textlightgrey

ElementName

TextDavid

Textlightblue

ElementName

TextRoger

Textlightyellow

child::Member[1]context node (.)

child::Name

The expression "*" means any element node

./child::Member[1]/child::*

Starting from the context node, navigate toa child node - the first Member. Now, usingthat Member as the context node, navigateto all child element nodes - the Name nodeand the FavoriteColor node.

Don't forget to use two colons

• Remember, it is child::Member

• It is NOT child:Member– The XSLT processor will think that you mean a

Member element in a "child namespace"!

Descendant Axis

• The descendant axis is used to navigate to a node that is "under" the context node. The node could be a child node, a grandchild, a great-grandchild, etc.

./descendant::Name[1]

Starting from the context node, navigate to a descendant node - the first Name descendant. (Note: descendants of a node are considered in document order. Thus, this example says to navigate, from the context node, to the first Name element in the document.)

Load this XML Documentinto Oxygen

<?xml version="1.0"?><FitnessCenter> <Member level="platinum"> <Name>Jeff</Name> <FavoriteColor>lightgrey</FavoriteColor> </Member> <Member level="gold"> <Name>David</Name> <FavoriteColor>lightblue</FavoriteColor> </Member> <Member level="platinum"> <Name>Roger</Name> <FavoriteColor>lightyellow</FavoriteColor> </Member> <Employee> <Name>Erika</Name> </Employee> <Employee> <Name>Linda</Name> </Employee> <CEO> <Name>Jack</Name> </CEO> <VP> <Name>Dora</Name> </VP></FitnessCenter>

See FitnessCenter_v3.xml in the example000 folder.

Establish the Context Node

Make this the context node.

Attribute Axis

• The attribute axis is used to navigate to an attribute of the context node.

./child::Member[1]/attribute::level

Starting from the context node, navigate toa child node - the first Member. Now, usingthat Member as the context node, navigateto an attribute node - the level attribute.Note: if you want to select all attributes then use: attribute::*

Self Axis

• The self axis is used to select the current node (i.e., “here”).

./child::*[not(self::Member)]/child::Name

Starting from the context node, navigate toall child element nodes that are not Membernodes. From each of the selected nodes,navigate to a child node - Name.This XPath expression will navigate to theName nodes containing: Erika, Linda, Jack,Dora.

Incorrect

./child::*[not(Member)]/child::Name

This says: given the context node, determine if there is not a Member node within it.This XPath expression will navigate to theName nodes containing: Jeff, David, Roger,Erika, Linda, Jack, Dora.

Equivalent!

./*[not(Member)]/Name ./child::*[not(child::Member)]/child::Name

Both of these expressions say: starting at the context node go to allchild element nodes that do not have a Member child. Then, usingthe elements selected, go to the child Name node.

The first uses the abbreviated XPath notation. The second uses the expanded XPath notation. Here we see that the expanded notation reduces ambiguity!

Do Lab4

Descendant-or-self Axis

• This axis is used to navigate to the current node and all its descendants.

descendant-or-self::*

Give the context node and all ofthe element nodes that are under it.

Following-sibling Axis

• This axis is used to navigate to a node that is "parallel" to the context node (i.e., at the same hierarchy level) and follows the context node.

./child::Member[1]/following-sibling::Employee[2]

Starting from the context node, navigate toa child node - the first Member. Now, usingthat Member as the context node, navigateto the second Employee sibling that follows theMember node.

<Member> <Name>Jeff</Name> <FavoriteColor>lightgrey</FavoriteColor></Member><Member> <Name>David</Name> <FavoriteColor>lightblue</FavoriteColor></Member><Member> <Name>Roger</Name> <FavoriteColor>lightyellow</FavoriteColor></Member><Employee> <Name>Erika</Name></Employee><Employee> <Name>Linda</Name></Employee><CEO> <Name>Jack</Name></CEO><VP> <Name>Dora</Name></VP>

Document/

ElementMember

ElementName

TextJeff

Textlightgrey

ElementName

TextDavid

Textlightblue

ElementName

TextRoger

Textlightyellow

context node (.)

following-sibling

Note: a node is a following sibling of another node only if it has the same parent.Consquently, the Name and FavoriteColor nodes in Member[2] and Member[3]are not following-siblings of the Name in Member[1].

Following Axis

• This axis is used to navigate to the nodes that follow the context node.

./child::Member[1]/following::Name

Starting from the context node, navigate toa child node - the first Member. Now, usingthat Member as the context node, navigateto all the Name nodes that follow.This XPath expression will navigate to theName nodes containing: David, Roger.

Document/

ElementMember

ElementName

TextJeff

Textlightgrey

ElementName

TextDavid

Textlightblue

ElementName

TextRoger

Textlightyellow

child::Member[1]

following nodes

context node (.)

Document/

ElementA

ElementB

ElementC

ElementD

ElementE

ElementH

ElementI

ElementJ

Text TextElementF

ElementG

Context node

following nodes

<?xml version="1.0"?><A> <B> <D>...</D> <E> <F>…</F> <G>…</G> </E> <H>...</H> </B> <C> <I>…</I> <J>…</J> </C></A>

following::E

Parent Axis

• This axis is used to navigate to the parent of the context node.

./parent::FitnessCenter

Starting from the context node, navigate tothe parent, provided it is <FitnessCenter>.Suppose that we wanted to navigate to theparent, whatever it is. We would use this: parent::*. Note: if the context node is an attribute node, then its parent is the element node that the attribute is attached to.

Suppose that Member[1] is the context node

Preceding-sibling axis

• This axis is used to navigate to a node that is "parallel" to the context node (i.e., at the same hierarchy level) and precedes the context node.

./child::*[last()]/preceding-sibling::Member[1]

Starting from the context node, navigate toa child node - the last element node. Now, usingthat node as the context node, navigateto the first Member sibling that precedes it.

<Member> <Name>Jeff</Name> <FavoriteColor>lightgrey</FavoriteColor></Member><Member> <Name>David</Name> <FavoriteColor>lightblue</FavoriteColor></Member><Member> <Name>Roger</Name> <FavoriteColor>lightyellow</FavoriteColor></Member><Employee> <Name>Erika</Name></Employee><Employee> <Name>Linda</Name></Employee><CEO> <Name>Jack</Name></CEO><VP> <Name>Dora</Name></VP>

Preceding Axis

• This axis is used to navigate to all the nodes that come before the context node.

<Member level="platinum"> <Name>Jeff</Name> <FavoriteColor>lightgrey</FavoriteColor></Member><Member level="gold"> <Name>David</Name> <FavoriteColor>lightblue</FavoriteColor></Member><Member level="silver"> <Name>Roger</Name> <FavoriteColor>lightyellow</FavoriteColor></Member>

./child::Member[last()]/preceding::Name

Starting from the context node, navigate toa child node - the last Member. Now, usingthat Member as the context node, navigateto all the Name nodes that precede.This XPath expression will navigate to theName nodes containing: David, Jeff.

Load this XML document into Oxygen

<?xml version="1.0"?><Book> <Title>Origin of Wealth</Title> <Chapter> <Title>The Paradigm Shift</Title> <Section> <Title>The Question</Title> <Para>I sat perched on …</Para> </Section> </Chapter></Book>

Make this the context node

This is Book.xml in the example000 folder

Ancestor Axis

• This axis is used to navigate to an ancestor node.

ancestor::*[2]/child::Title

Navigate to the grandparentand from there navigate to thechild Title node.

<Title>The Paradigm Shift</Title>

Result:

Ancestor-or-self Axis

• This axis is used to navigate to the current node and its ancestors.

ancestor-or-self::*

Select the current node and all its ancestors

text() is a function that selects text nodes

ElementMember

ElementName

TextJeff

Textlightgrey

Text"cr "

Text"cr"

Suppose that the context node is the Member element. Then this expression: text()will result in selecting the 3 child text nodes.

Note: cr = carriage return

Document/

ElementMember

ElementName

TextJeff

Textlightgrey

ElementName

TextDavid

Textlightblue

ElementName

TextRoger

Textlightyellow

/FitnessCenter/Member[1]/Name selects

Document/

ElementMember

ElementName

TextJeff

Textlightgrey

ElementName

TextDavid

Textlightblue

ElementName

TextRoger

Textlightyellow

/FitnessCenter/Member[1]/Name/text() selects

node() is a function that selectstext, element, document, comment and PI nodes

ElementMember

ElementName

CommentThis is a comment

TextJeff

Text"cr "

Suppose that the context node is the Member element. Then this expression: node() will result in selecting the 4 child text nodes, the 1 element node, the 1 comment node, and the 1 PI node.

PIfoo="blah"

Text"cr"

Examples

child::para selects the para element children of the context node.child::* selects all the element children of the context node.child::text() selects all text node children of the context node.child::node() selects all the children of the context node, whatever their node type (i.e., text node, element node, document (/) node, comment node, or processing instruction node)attribute::name selects the name attribute of the context node.attribute::* selects all the attributes of the context node.parent::node() selects the parent of the context node. If the context node is an attribute node, this expression returns the element node to which the attribute is attached.descendant::para selects all the para element descendants of the context node.ancestor::div selects all div ancestors of the context node.ancestor-or-self::div selects the div ancestors of the context node and, if the context node is a div element, the context node as well.descendant-or-self::para selects the para element descendants of the context node and, if the context node is a para element, the context node as well.self::para selects the context node if it is a para element, and otherwise nothing.

Expanded Notation

• The expanded notation has several advantages:– Nonambiguous: it makes it very clear how you are

navigating through the XML tree.

– Powerful: it provides the means to navigate the XML tree in pretty much every way that you might desire.

• But it has a disadvantage:– Verbose: your XPath expressions can get pretty long,

even for simple things.

Abbreviated Notation

• We will now look at the abbreviated notation.• Here are its advantages:

– Brevity: the XPath expressions are much shorter.

• Here are its disadvantages:– Ambiguous: sometimes the expression can be misinterpreted,

such as we saw with this expression: ./*[not(Member)]/Name– Less powerful: there are some things that you simply can't

do with the abbreviated notation, e.g., navigate to ancestors, navigate to preceding siblings, navigate to following siblings.

Omitting the Axis

• Recall that when using the expanded notation you provide 3 things:– An axis (e.g., child, ancestor, descendant)– A pair of colons (i.e., ::)– A node name (or "*" if you wish to navigate to all

element or attribute nodes)

• That is, here is the general form: axis::node

• The abbreviated notation allows you to omit the axis and colons. What is the default axis?

Default Axis

• The default axis is child. Thus, these forms are equivalent:

./child::*[not(Member)]/child::Name ./child::*[not(child::Member)]/child::Name

No axis is specified. Consequently, an XPath processorwill use the default axis: child. Thus, it will treat this as:child::Member

Member[Name] child::Member[child::Name]is equivalent to:

Examples of using the Abbreviated Notation and the Default Axis

./child::Member[1]/child::Name ./Member[1]/Name

expanded notation abbreviated notation

./child::*[not(child::Member)]/child::Name ./*[not(Member)]/Name

@ is the abbreviated notation for the attribute axis

./child::Member[1]/attribute::level ./Member[1]/@level

Do Lab5

Load this XML Document into Oxygen

<?xml version="1.0"?><Book> <para>paragraph #1</para> <para>paragraph #2</para> <para>paragraph #3</para> <Chapter> <para>paragraph #4</para> <para>paragraph #5</para> <Section> <para>paragraph #6</para> </Section> </Chapter></Book>

This is Book_v2.xml in the example000 folder

// is the abbreviated notation for descendant-or-self::node()/

./descendant-or-self::node()/child::para.//para

expanded notationabbreviated notation

These expressions both say: starting from the context node select allthe descendant nodes as well as the context node. Now, for each ofthem select the child para elements. In other words, this results inselecting all para elements that descend from the context node.

What will be the result?

Result:<para>paragraph #1</para><para>paragraph #2</para><para>paragraph #3</para><para>paragraph #4</para><para>paragraph #5</para><para>paragraph #6</para>

./descendant-or-self::node()/child::para

What will be the result?

.//para[1]

Result:<para>paragraph #1</para><para>paragraph #4</para><para>paragraph #6</para>

Let's see why

descendant-or-self::node()/child::para[1].//para[1]

Select all nodes that descend from the context node,including the context node. For each of them, selectthe first para child element.

is equivalent to:

Contrast with this!

./descendant::para[1]

Result:<para>paragraph #1</para>

Let's see why

./descendant::para[1]

Select all para elements that descend from the context node. Then select the first one.

Lesson Learned

.//para[1] ./descendant::para[1]

Not equivalent!

Do Lab6

.. is an abbreviation of parent::node()

parent::node()..

parent::node()/child::para../para

. is an abbreviation of self::node()

. self::node()

Good Example<Member level="platinum"> <Name>Jeff</Name> <FavoriteColor>lightgrey</FavoriteColor></Member><Member level="gold"> <Name>David</Name> <FavoriteColor>lightblue</FavoriteColor></Member><Member level="platinum"> <Name>Roger</Name> <FavoriteColor>lightyellow</FavoriteColor></Member>

Member[FavoriteColor='lightblue']

<Member level="gold"> <Name>David</Name> <FavoriteColor>lightblue</FavoriteColor></Member>

Let's see its Expanded Notation

Member[FavoriteColor='lightblue']

child::Member[child::FavoriteColor='lightblue']

Select all Member child elements which have a FavoriteColorchild element whose value is lightblue.

Examplespara selects the para element children 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.@* 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 grandchildren of the context node./book/chapter[5]/section[2] selects the second section of the fifth chapter of the book whose parent is the document node.chapter//para selects the para element descendants of all the chapter element children of the context node.//para selects all the para element descendants in the document//@version selects all the version attribute nodes in the document//list/member selects all the child member elements of all the list elements..//para selects all para element descendants of the context node... selects the parent of the context node.../@lang selects the lang attribute of the parent of the context node.para[@type='warning'] selects all para children of the context node that have a type attribute with value warning.chapter[title='Introduction'] selects the chapter children of the context node that have one or more title children whose value equals Introduction.chapter[title] selects the chapter children of the context node that have one or more title children.employee[@secretary and @assistant] selects all the employee children of the context node that have both a secretary attribute and an assistant attribute.Member[Name='Jeff' or Name='Roger']/FavoriteColor selects all FavoriteColor children of Member elements that have a Name child element equal to Jeff or Roger.

Summary

Expanded Notation Abbreviated Notationchild::para paradescendant::paraattribute::level @levelself::node() .descendant-or-self::node()/child::para .//parafollowing-sibling::parafollowing::nameparent::node() ..preceding-sibling::Memberpreceding::Nameancestor::FitnessCenterancestor-or-self::Title

Predicates

• A predicate consists of an expression, called a predicate expression, enclosed in square brackets.

• A predicate serves to filter a sequence--retaining some items and discarding others.

• Those items for which the predicate evaluates to true are retained, and those for which the predicate evaluates to false are discarded.

Predicates

path-expression[predicate-expression]

The predicate-expressionis evaluated within the contextprovided by the path-expression.The result of evaluating thepredicate expression is a boolean value:true or false.

Numeric Predicates

• If the predicate expression is a number, then the predicate evaluates to true if the number equals the context position.

• Consider this XPath: Member[2]

• The path expression yields this sequence:

The predicate is evaluated against each of these items. Since the predicate is a number it will becompared against each item's context position. For the first item its context position is 1 and 1 = 2so the first item is discarded. For the second item its context position is 2 and 2 = 2 so the second itemis retained. For the third item its context position is 3 and 3 = 2 so the third item is discarded.

Element Predicates

• If the predicate expression is an element node, then the predicate evaluates to true if the node exists. (Conversely, a predicate expression which evaluates to an empty sequence evaluates to false)

• Consider this predicate expression: Member[FavoriteColor]• Suppose the Member path expression yields this sequence:

<Member> <Name>David</Name></Member>

Note that the second Member does not have a FavoriteColor. The predicate is evaluated against each of these items. Since the predicate is an element node the XSLT processor will determine ifthe node exists for each item. For the first Member there does exist a FavoriteColor child element soit is retained. For the second Member there does not exist a FavoriteColor child element so it isdiscarded. For the third Member there does exist a FavoriteColor child element so it is retained.

Boolean Predicates

• If the predicate expression is a boolean expression, then the predicate evaluates to true if the boolean expression evaluates to true.

• Consider this XPath: Member[Name = 'Jeff']• Suppose the Member path expression yields this

sequence:<Member> <Name>Jeff</Name> <FavoriteColor>lightgrey</FavoriteColor></Member>

The predicate is evaluated against each of these items. The first Member has a child Name elementwith a value equal to Jeff, so it is retained. The second and third Member elements have a child Nameelement, but with a value other than Jeff, so they are discarded.

Multiple Predicates

• It is legal to have multiple predicates:

path-expression[predicate-expression1] [predicate-expression2]

{sequence of nodes selected by path-expression}

filter using predicate-expression1

{sequence of nodes after filtering with predicate-expression1}

filter using predicate-expression2

{sequence of nodes after filtering with predicate-expression2}

• They are evaluated as follows:

<?xml version="1.0"?><FitnessCenter> <Member level="platinum"> <Name>Jeff</Name> <FavoriteColor>lightgrey</FavoriteColor> </Member> <Member level="gold"> <Name>David</Name> <FavoriteColor>lightblue</FavoriteColor> </Member> <Member level="platinum"> <Name>Roger</Name> <FavoriteColor>lightyellow</FavoriteColor> </Member></FitnessCenter>

Member[@level='platinum'][2]

<Member level="platinum"> <Name>Roger</Name> <FavoriteColor>lightyellow</FavoriteColor></Member>

Member[2] [@level='platinum']

-- empty --

Order Matters!

Do Lab7

Arithmetic Expressions

• XPath provides these arithmetic operators:

+ (addition)- (subtraction and unary negation)* (multiplication)div (division)mod (modulus, i.e., the remainder from division)

Example: child::Cost * 2 (multiply the value of the Cost child element by 2)Example: position() mod 2 = 0 (this expression will evaluate to true for context items at even positions, and false otherwise)

Boolean Operators

• XPath provides these boolean operators:

andornot

Example: child::Cost and child::Member (This expression will evaluate to true only if there exists a Cost child element

and a Member child element)Example: ((child::Cost * 2 = 50) and (child::Member))

Parenthesized Expressions

• Use parentheses to ensure that your expressions are evaluated in the order you desire.

Example: (child::Cost and child::Member) or (child::Cost and child::Test) This expression will evaluate to true if there exists a Cost child element and a Member child element, or there exists a Cost child element and a Test child element.

Comparison Operators

• These general comparison operators are available:

= | != | < | <= | > | >=

Load this XML Documentinto Oxygen<?xml version="1.0"?><FitnessCenter> <Member> <Name>Jeff</Name> <Age>39</Age> </Member> <Member> <Name>David</Name> <Age>33</Age> </Member> <Member> <Name>Roger</Name> <Age>36</Age> </Member></FitnessCenter>

This is FitnessCenter_v4.xml in the example000 folder.

General Comparison

Member/Age = 39Member/Age != 20Member/Age < 40Member/Age <= 40Member/Age > 30Member/Age >= 30

<?xml version="1.0"?><FitnessCenter> <Member> <Name>Jeff</Name> <Age>39</Age> </Member> <Member> <Name>David</Name> <Age>33</Age> </Member> <Member> <Name>Roger</Name> <Age>36</Age> </Member></FitnessCenter>

Result:Member/Age = 39 … trueMember/Age != 20 … trueMember/Age < 40 … trueMember/Age <= 40 … trueMember/Age > 30 … trueMember/Age >= 30 … true

Note that I am not specifying a specific Member. Consequently, I am comparing all Member Ages.

General Comparison<?xml version="1.0"?><FitnessCenter> <Member id="1" level="platinum"> <Name>Jeff</Name> <Phone type="home">555-1234</Phone> <Phone type="work">555-4321</Phone> <FavoriteColor>lightgrey</FavoriteColor> <MembershipFee>340</MembershipFee> <Age>39</Age> </Member> <Member id="2" level="gold"> <Name>David</Name> <Phone type="home">383-1234</Phone> <Phone type="work">383-4321</Phone> <FavoriteColor>lightblue</FavoriteColor> <MembershipFee>500</MembershipFee> <Age>33</Age> </Member> <Member id="3" level="platinum"> <Name>Roger</Name> <Phone type="home">888-1234</Phone> <Phone type="work">888-4321</Phone> <FavoriteColor>lightyellow</FavoriteColor> <MembershipFee>340</MembershipFee> <Age>36</Age> </Member></FitnessCenter>

Member/Age = 39?

Does there exist an Age valuethat equals 39? Yes!

Member/Age = 39 is equivalent to: (Member[1]/Age = 39) or (Member[2]/Age = 39) or (Member[3]/Age = 39)

Use General Comparison to Compare Two Sequences

<?xml version="1.0"?><FitnessCenter> <Member> <Name>Jeff</Name> <Age>39</Age> <Salary units="thousands">20</Salary> </Member> <Member> <Name>David</Name> <Age>33</Age> <Salary units="thousands">39</Salary> </Member> <Member> <Age>36</Age> <Salary units="thousands">45</Salary> </Member></FitnessCenter>

Member/Age = Member/Salary

Result: Member/Age = Member/Salary … true

"Is there is an Age valuewhich equals a Salary value."

All Combinations of Sequence Values are Compared

Age393336

Salary203945

XPath Functions• XPath provides a lot of functions for you to use. We have

already seen some, such as position(), last(), text(), node(), count(), and translate().

• Here's how the XPath functions are categorized:– String functions: those functions which when evaluated return a string.

– Boolean functions: those functions which when evaluated return a boolean value (true or false).

– Number functions: those functions which when evaluated return a number.

– Node functions: those functions which when evaluated return a node.

– Namespace functions: those functions that are intended for use with namespaces.

Notation

• Some functions have optional arguments. For example, the name function has an optional argument. I will use "?" after the argument to indicate that it is optional, e.g., name(node?).

• Some functions allow zero or more occurrences of an argument. For example, the concat function allows zero or more strings after the first two arguments. I will use "*" after the argument to indicate zero or more occurrences, e.g.,

concat(string, string, string*)

String Functions

• name(node?) - this function returns the name of a node. If no argument is provided then it returns the name of the context item.

• string(object?) - If object is a node this function returns the value of the node (if the node is not a leaf node then it concatenates the values of all the leaf nodes that are under it)

• concat(string, string, string*) - this function concatenates all its arguments. There must be at least two arguments.

Example: concat(‘Name; ’, child::Name)

String Functions (cont.)

• substring-before(string1, string2) - this function returns a string representing the substring of string1 that precedes the first occurrence of string2, or the empty string if string1 does not contain string2.

• substring-after(string1, string2) - this function returns a string representing the substring of string1 that follows the first occurrence of string2, or the empty string if string1 does not contain string2.

Example: substring-before(child::Phone, '555')

Example: substring-after(child::Phone, '555')

String Functions (cont.)

• substring(string, number1, number2?) - this function returns a string representing the substring of string starting at the position specified by number1 with the length specified by number2. If number2 is not specified then it returns the substring starting at the position specified by number1, and continuing to the end of string.

• translate(string1, string2, string3) - this function returns a string obtained by converting each character in string1 that is contained in string2 into the character in string3 that is at the same position as in string2. For those characters in string1 which are not present in string2, they are returned untouched.

substring(string, num1, num2?)

Example: substring('1234567890', 2, 5) returns '23456'

String Functions (concluded)

• normalize-space(string?) - this function returns a string obtained by trimming leading and trailing whitespaces (space, carriage return, tab, linefeed) off the argument, and replacing sequences of whitespaces by a single space. If the argument is omitted, it defaults to the context node converted to a string. In other words, these two function calls are equivalent:

normalize-space()

is equivalent to:

normalize-space(string(self::*))

Boolean Functions

• starts-with(string1, string2) - this function returns true if string1 starts with string2, and otherwise returns false.

• contains(string1, string2) - this function returns true if string1 contains string2, and otherwise returns false.

Example: starts-with(child::Phone, '555')

Example: contains(child::FavoriteColor, 'blue')

Boolean Functions (concluded)

• boolean(object) - this function converts object to a boolean value as follows:– if object is a number (not zero) then the function returns true, if object is zero

then the function returns false.

– if object is a node which exists then the function returns true; if the node does not exist then the function returns false.

– if object is a string of length greater than zero then the function returns true; otherwise the function returns false.

• true() - this function returns true• false() - this function returns false• lang(string) - this function returns true if the xml:lang value of the

context item matches string, and false otherwise. (Recall the default value of xml:lang is 'EN')

Number Functions

• position() - this function returns an integer, representing the position of the context item within a sequence of items.

• last() - this function returns an integer, representing the context size.

• count(node sequence) - this function returns an integer representing the number of nodes in node sequence.

• string-length(string?) - this function returns an integer representing the number of characters in string. If the argument is omitted, it defaults to the context node converted to a string.

Example: string-length(child::FavoriteColor)

Number Functions (concluded)

• number(object?) - this function converts object to a number as follows:– if object is a number then it returns the number.– if object is a boolean true then it returns 1, if object is a boolean false then

it returns 0.– if object is a node then it returns the value of the node.

• sum(node sequence) - this functions sums up the values of all the nodes that are identified by node sequence.

• floor(number) – truncates the number.• ceiling(number) – next integer.• round(number) - rounds the number, e.g., 12.5 rounds to 13, -12.5

rounds to -12.

floor(), ceiling(), round()

Example: floor(2.5) returns 2

Example: ceiling(2.5) returns 3

Example: round(2.3) returns 2

Node Functions

• text() - this function matches on any text node.

• node() - this function matches on any text, element, document, comment, or PI node.

• id(node id) - this function returns the node with an ID value equal to node id.

Example: id(child::GuestAuthor/BookForSigning/@isbn-ref) will return the element which has an ID value that matches isbn-ref.

Open this file in Oxygen

<?xml version="1.0"?><FitnessCenter xmlns="http://www.gym.com"> <Member level="platinum"> <Name>Jeff</Name> <Phone type="home">555-1234</Phone> <Phone type="work">555-4321</Phone> <FavoriteColor>lightgrey</FavoriteColor> </Member></FitnessCenter>

This is FitnessCenter_v5.xml in the example000 folder.

Establish this as the context node

Namespace Terminology

{http://www.gym.com}Member

Expanded name = The combination of the namespace URI and the local name

Local name

Namespace URI

Namespace Terminology (cont.)

<gym:FitnessCenter xmlns:gym="http://www.gym.com"> <gym:Member> …</gym:FitnessCenter>

<gym:Member>

prefix

local-name(node?)

• This is an XPath function which returns a string, corresponding to the local name of the node.

local-name(.)

Result:Name

namespace-uri(node?)

• This is an XPath function which returns a string corresponding to the namespace URI of the node.

namespace-uri(.)

Result:http://www.gym.com

Congratulations!

• You now know everything there is to know about XPath 1.0!

• We have covered the entire XPath specification. We have left no stone unturned.

1 xpath 1.0 roger l. costello 6 march 2010

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long xpath expressions

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