1 Quick Intro to XPath Roger L. Costello 14 December, 2012.

1

Quick Intro to XPath

Roger L. Costello14 December, 2012

2

Objective

• XML Schema 1.1 uses XPath a lot, so if you don't know XPath then you're at a disadvantage.

• The purpose of this short tutorial is to teach you enough XPath that you won't be at a disadvantage.

3

XPath is not a standalone language

• XPath requires a host language. There are currently several XML languages that host XPath.

4

XPath is not a standalone language

XPath

XSLT

XQuery

XMLSchemas

XPointer

Schematron

5

Document/

PI<?xml version=“1.0”?>

ElementFitnessCenter

ElementMember

ElementMember

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

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Terminology - node

Document/



ElementMember

ElementMember

ElementMember

ElementName


TextJeff

Textlightgrey

ElementName


TextDavid

Textlightblue

ElementName


TextRoger

Textlightyellow

Document nodeProcessing Instruction (PI) node

Element nodes

Text nodes

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Document/



ElementMember

ElementMember

ElementMember

ElementName


TextJeff

Textlightgrey

ElementName


TextDavid

Textlightblue

ElementName


TextRoger

Textlightyellow

With respect to this node, these are its children

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Document/



ElementMember

ElementMember

ElementMember

ElementName


TextJeff

Textlightgrey

ElementName


TextDavid

Textlightblue

ElementName


TextRoger

Textlightyellow

These are its descendant nodes

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Document/



ElementMember

ElementMember

ElementMember

ElementName


TextJeff

Textlightgrey

ElementName


TextDavid

Textlightblue

ElementName


TextRoger

Textlightyellow

This is the context node

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Document/



ElementMember

ElementMember

ElementMember

ElementName


TextJeff

Textlightgrey

ElementName


TextDavid

Textlightblue

ElementName


TextRoger

Textlightyellow

That's its parent

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Document/



ElementMember

ElementMember

ElementMember

ElementName


TextJeff

Textlightgrey

ElementName


TextDavid

Textlightblue

ElementName


TextRoger

Textlightyellow

Those are its ancestors

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Document/



ElementMember

ElementMember

ElementMember

ElementName


TextJeff

Textlightgrey

ElementName


TextDavid

Textlightblue

ElementName


TextRoger

Textlightyellow

It has 2 siblings

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Document/



ElementMember

ElementMember

ElementMember

ElementName


TextJeff

Textlightgrey

ElementName


TextDavid

Textlightblue

ElementName


TextRoger

Textlightyellow

They are following-siblings

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Document/



ElementMember

ElementMember

ElementMember

ElementName


TextJeff

Textlightgrey

ElementName


TextDavid

Textlightblue

ElementName


TextRoger

Textlightyellow

It has no preceding-siblings

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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(), etc.) to facilitate the above.

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Document/


ElementDocument

ElementPara

ElementPara

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”

Attributeclassification=“unclassified”

See document.xml in the xpathfolder, within the examples folder.

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Execute XPath using Oxygen XML

Type your XPath expression here

Change this to XPath 1.0

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Use XPath Builderfor long XPathexpressions

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Please Run the XPath Expressions

• The following slides contain XPath expressions.

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

• First, copy the XML document on slide 16, save it to a file, then drag and drop the file into Oxygen XML.

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Select all Para Elements

/Document/Para

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/Document/Para

This is an absolute XPath expression

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Establish a Context Node

Click on this to establish it as the "context node"(any XPath expressions will be relative to it)

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Relative XPath Expression

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

Para

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Select all Para Elements

//Para

descendents

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Select the first Para

//Para[1]

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Select the last Para

//Para[last()]

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Select the classification attribute of the first Para

//Para[1]/@classification

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Is the Document element’s classification top-secret?

/Document/@classification = 'top-secret'

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Is the Document element’s classification top-secret or

secret?

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

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A or BA and Bnot(A)

Logical Operators

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Select all Para’s with a secret classification

//Para[@classification = 'secret']

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Check that no Para has a top-secret classification

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

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Establish a New Context Node

Make the second Para the context node

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Select the Following Siblings

following-sibling::*

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Select the FirstFollowing Sibling

following-sibling::*[1]

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Add Another Element

Add this <Test> element after the last Para

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Select the Following Para Siblings

following-sibling::Para

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Select all Following Siblings

following-sibling::*

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Select all Preceding Siblings

preceding-sibling::*

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Make Document the Context

Click on Document to make it thecontext node.

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Equivalent!

Para[1]

child::Para[1]

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Make Para[2] the context

Establish this as the context node.

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Get parent element's classification

../@classification

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Equivalent!

../@classification

parent::*/@classification

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Axis

following-siblingpreceding-siblingchildparentancestordescendentself

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Count the number of Para elements

count(//Para)

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Count the number of Para elements with secret

classification

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

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Does the first Para element contain the string

“SCRIPT”?

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

49

Select all nodes containing the string “SCRIPT”

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

The node() function matches on these nodes: - element - text - comment - processing instructions (PIs)Note that it does not match on these nodes: - attribute - document

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Count the number of nodes containing the

string “SCRIPT”

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

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Select the first 20 characters of the first Para

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

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

string-length(//Para[1])

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

Convert Document’s classification to lowercase

54

Add a new <Cost> element

Add this element and establishDocument as the context node.

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Multiply Cost by 2

Cost * 2

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N mod X = the remainder of dividing N by X

Cost mod 2

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Arithmetic Operators

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

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Set this to XPath 2.0

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Does Document’s classification match one in

Classifications.xml?

/Document/@classification = doc('Classifications.xml')/Classifications/li

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Do the first two Para's have the same classification?

Para[1]/@classification eq Para[2]/@classification

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eq means equalne means not equallt means less thangt means greater thanle means less than or equal toge means greater than or equal to

Boolean Operators

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if Document's classification is top-secret then there can be no Para with a classification

not equal to top-secret

if (/Document/@classification eq 'top-secret') then not(//Para[@classification ne 'top-secret']) else true()

63

Two built-in functions

true()

false()

64

Cast a value to a numeric type

number(Cost)

65Check that Document's children are: multiple Para's,

1 Test, and 1 Cost (and nothing else)

Para[2] and Test and Cost and empty(* except (Para, Test[1], Cost[1]))

66

The sum() function

<?xml version="1.0"?><numbers> <number>23</number> <number>5</number> <number>-41</number> <number>50</number> <number>12</number></numbers>

sum(//number) returns 49.0

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Check that every Publisher has a string-length le 140

<BookStore> <Book> <Title>My Life and Times</Title> <Author>Paul McCartney</Author> <Date>1998</Date> <ISBN>1-56592-235-2</ISBN> <Publisher>McMillin Publishing</Publisher> <Author>John Ghostwriter</Author> </Book> <Book> <Publisher>Dell Publishing Co.</Publisher> <Author>Richard Bach</Author> <Date>1977</Date> <ISBN>0-440-34319-4</ISBN> <Title>Illusions The Adventures of a Reluctant Messiah</Title> </Book> <Book> <ISBN>0-06-064831-7</ISBN> <Title>The First and Last Freedom</Title> <Author>J. Krishnamurti</Author> <Date>1954</Date> <Publisher>Harper & Row</Publisher> </Book></BookStore>

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Check that every Publisher has a string-length le 140

every $i in //Publisher satisfies string-length($i) le 140

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The XPath every expression

• The form of the every expression is:every variable in sequence satisfies boolean expression

• The result of the expression is either true or false.

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Equivalent

every $i in //Publisher satisfies string-length($i) le 140

not(//Publisher[string-length(.) gt 140])

1 Quick Intro to XPath Roger L. Costello 14 December, 2012.

Documents

xml document

xpath roger

capabilities of xpath

parent slide

context node slide

node values xpath

xpath folder

alarm ready