1 quick intro to xpath roger l. costello 14 december, 2012
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1
Quick Intro to XPath
Roger L. Costello14 December, 2012
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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.
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XPath is not a standalone language
• XPath requires a host language. There are currently several XML languages that host XPath.
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XPath is not a standalone language
XPath
XSLT
XQuery
XMLSchemas
XPointer
Schematron
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Document/
PI<?xml version=“1.0”?>
ElementFitnessCenter
ElementMember
ElementMember
ElementMember
ElementName
ElementFavoriteColor
TextJeff
Textlightgrey
ElementName
ElementFavoriteColor
TextDavid
Textlightblue
ElementName
ElementFavoriteColor
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/
PI<?xml version=“1.0”?>
ElementFitnessCenter
ElementMember
ElementMember
ElementMember
ElementName
ElementFavoriteColor
TextJeff
Textlightgrey
ElementName
ElementFavoriteColor
TextDavid
Textlightblue
ElementName
ElementFavoriteColor
TextRoger
Textlightyellow
Document nodeProcessing Instruction (PI) node
Element nodes
Text nodes
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Document/
PI<?xml version=“1.0”?>
ElementFitnessCenter
ElementMember
ElementMember
ElementMember
ElementName
ElementFavoriteColor
TextJeff
Textlightgrey
ElementName
ElementFavoriteColor
TextDavid
Textlightblue
ElementName
ElementFavoriteColor
TextRoger
Textlightyellow
With respect to this node, these are its children
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Document/
PI<?xml version=“1.0”?>
ElementFitnessCenter
ElementMember
ElementMember
ElementMember
ElementName
ElementFavoriteColor
TextJeff
Textlightgrey
ElementName
ElementFavoriteColor
TextDavid
Textlightblue
ElementName
ElementFavoriteColor
TextRoger
Textlightyellow
These are its descendant nodes
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Document/
PI<?xml version=“1.0”?>
ElementFitnessCenter
ElementMember
ElementMember
ElementMember
ElementName
ElementFavoriteColor
TextJeff
Textlightgrey
ElementName
ElementFavoriteColor
TextDavid
Textlightblue
ElementName
ElementFavoriteColor
TextRoger
Textlightyellow
This is the context node
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Document/
PI<?xml version=“1.0”?>
ElementFitnessCenter
ElementMember
ElementMember
ElementMember
ElementName
ElementFavoriteColor
TextJeff
Textlightgrey
ElementName
ElementFavoriteColor
TextDavid
Textlightblue
ElementName
ElementFavoriteColor
TextRoger
Textlightyellow
That's its parent
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Document/
PI<?xml version=“1.0”?>
ElementFitnessCenter
ElementMember
ElementMember
ElementMember
ElementName
ElementFavoriteColor
TextJeff
Textlightgrey
ElementName
ElementFavoriteColor
TextDavid
Textlightblue
ElementName
ElementFavoriteColor
TextRoger
Textlightyellow
Those are its ancestors
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Document/
PI<?xml version=“1.0”?>
ElementFitnessCenter
ElementMember
ElementMember
ElementMember
ElementName
ElementFavoriteColor
TextJeff
Textlightgrey
ElementName
ElementFavoriteColor
TextDavid
Textlightblue
ElementName
ElementFavoriteColor
TextRoger
Textlightyellow
It has 2 siblings
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Document/
PI<?xml version=“1.0”?>
ElementFitnessCenter
ElementMember
ElementMember
ElementMember
ElementName
ElementFavoriteColor
TextJeff
Textlightgrey
ElementName
ElementFavoriteColor
TextDavid
Textlightblue
ElementName
ElementFavoriteColor
TextRoger
Textlightyellow
They are following-siblings
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Document/
PI<?xml version=“1.0”?>
ElementFitnessCenter
ElementMember
ElementMember
ElementMember
ElementName
ElementFavoriteColor
TextJeff
Textlightgrey
ElementName
ElementFavoriteColor
TextDavid
Textlightblue
ElementName
ElementFavoriteColor
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/
PI<?xml version=“1.0”?>
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')
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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
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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()
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Two built-in functions
true()
false()
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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]))
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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])
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