Xpath Notes

8/8/2019 Xpath Notes

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Processing instructions

Description

Processing instructions (PIs) allow documents to contain instructions for applications.

Well-formed documents

Processing instructions :

vscht

Documents with errors

Processing instruction must end with ?>:


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XMLDeclaration

Description

XML documents may, and should, begin with an XML declaration which specifies the version ofXML being used.

Well-formed documents

XML version specification :

This document conforms to the XML 1.0 specification.Encoding specification :

If encoding is not given UTF-8 is assumed

XPath 1.0 Tutorial

Back|Forward||Previous|Next

XPath is described in XPath 1.0 standard. In this tutorial selected XPath features aredemonstrated on many examples.

Standard excerpt:XPath is the result of an effort to provide a common syntax and semantics for functionality

shared between XSL Transformations and XPointer. The primary purpose ofXPath is to address

parts of anXML

document. In support of this primary purpose, it also provides basic facilitiesfor manipulation of strings, numbers and booleans. XPath uses a compact, non-XML syntax tofacilitate use ofXPath within URIs and XML attribute values. XPath operates on the abstract,

logical structure of an XML document, rather than its surface syntax. XPath gets its name fromits use of a path notation as in URLs for navigating through the hierarchical structure of an XML

document.

List ofXPaths

XPath as filesystem addressing

The basicX

Path syntax is similar to filesystem addressing. If the path starts with the slash / ,then it represents an absolute path to the required element./AAA

/AAA/CCC/AAA/DDD/BBB

Start with //If the path starts with // then all elements in the document which fulfill following criteria are

selected.


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//BBB//DDD/BBB

All elements: *The star * selects all elements located by preceeding path

/AAA/CCC/DDD/*

/*/*/*/BBB//*Further conditions inside []

Expresion in square brackets can further specify an element. A number in the brackets gives theposition of the element in the selected set. The function last() selects the last element in the

selection./AAA/BBB[1]

/AAA/BBB[last()]Attributes

Attributes are specified by @ prefix.//@id

//BBB[@id]//BBB[@name]

//BBB[@*]//BBB[not(@*)]

Attribute valuesValues of attributes can be used as selection criteria. Function normalize-space removes leading

and trailing spaces and replaces sequences of whitespace characters by a single space.//BBB[@id='b1']

//BBB[@name='bbb']//BBB[normalize-space(@name)='bbb']

Nodes countingFunction count() counts the number of selected elements

//*[count(BBB)=2]//*[count(*)=2]

//*[count(*)=3]Playing with names of selected elements

Function name() returns name of the element, the starts-with function returns true if the firstargument string starts with the second argument string, and the contains function returns true if

the first argument string contains the second argument string.//*[name()='BBB']

//*[starts-with(name(),'B')]//*[contains(name(),'C')]

Length of stringThe string-length function returns the number of characters in the string. You must use < as a

substitute for < and > as a substitute for > .//*[string-length(name()) = 3]

//*[string-length(name()) < 3]//*[string-length(name()) > 3]

Combining XPaths with |Several paths can be combined with | separator.


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//CCC | //BBB/AAA/EEE | //BBB

/AAA/EEE | //DDD/CCC | /AAA | //BBBChild axis

The child axis contains the children of the context node. The child axis is the default axis and it

can be omitted./AAA/child::AAA

/AAA/BBB/child::AAA/child::BBB

/child::AAA/BBBDescendant axis

The descendant axis contains the descendants of the context node; a descendant is a child or achild of a child and so on; thus the descendant axis never contains attribute or namespace nodes

/descendant::*/AAA/BBB/descendant::*

//CCC/descendant::*//CCC/descendant::DDD

Parent axisThe parent axis contains the parent of the context node, if there is one.

//DDD/parent::*Ancestor axis

The ancestor axis contains the ancestors of the context node; the ancestors of the context nodeconsist of the parent of context node and the parent's parent and so on; thus, the ancestor axis

will always include the root node, unless the context node is the root node./AAA/BBB/DDD/CCC/EEE/ancestor::*

//FFF/ancestor::*Following-sibling axis

The following-sibling axis contains all the following siblings of the context node./AAA/BBB/following-sibling::*

//CCC/following-sibling::*Preceding-sibling axis

The preceding-sibling axis contains all the preceding siblings of the context node/AAA/XXX/preceding-sibling::*

//CCC/preceding-sibling::*Following axis

The following axis contains all nodes in the same document as the context node that are after thecontext node in document order, excluding any descendants and excluding attribute nodes and

namespace nodes./AAA/XXX/following::*

//ZZZ/following::*Preceding axis

The preceding axis contains all nodes in the same document as the context node that are beforethe context node in document order, excluding any ancestors and excluding attribute nodes and

namespace nodes/AAA/XXX/preceding::*


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//GGG/preceding::*Descendant-or-self axis

The descendant-or-self axis contains the context node and the descendants of the context node/AAA/XXX/descendant-or-self::*

//CCC/descendant-or-self::*

Ancestor-or-self axisThe ancestor-or-self axis contains the context node and the ancestors of the context node; thus,the ancestor-or-self axis will always include the root node.

/AAA/XXX/DDD/EEE/ancestor-or-self::*//GGG/ancestor-or-self::*

Orthogonal axesThe ancestor, descendant, following, preceding and self axes partition a document (ignoring

attribute and namespace nodes): they do not overlap and together they contain all the nodes inthe document.

//GGG/ancestor::*//GGG/descendant::*

//GGG/following::*//GGG/preceding::*

//GGG/self::*//GGG/ancestor::* | //GGG/descendant::* | //GGG/following::* | //GGG/preceding::* |

//GGG/self::*Numeric operations

The div operator performs floating-point division, the mod operator returns the remainder from atruncating division. The floor function returns the largest (closest to positive infinity) number

that is not greater than the argument and that is an integer.The ceiling function returns thesmallest (closest to negative infinity) number that is not less than the argument and that is an

integer.//BBB[position() mod 2 = 0 ]

//BBB[ position() = floor(last() div 2 + 0.5) or position() = ceiling(last() div 2 + 0.5) ]//CCC[ position() = floor(last() div 2 + 0.5) or position() = ceiling(last() div 2 + 0.5) ]

XPath as filesystem addressing

The basic XPath syntax is similar to filesystem addressing. If the path starts with the slash / ,

then it represents an absolute path to the required element.

/AAASelect the root element AAA


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/AAA/CCC

Select all elements CCC which are children of the root element AAA

/AAA/DDD/BBB

Select all elements BBB which are children of DDD which are children of the root element AAA

Start with //

If the path starts with // then all elements in the document which fulfill following criteria areselected.

//BBB

Select all elements BBB


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//DDD/BBB

Select all elements BBB which are children of DDD

All elements: *

The star * selects all elements located by preceeding path

/AAA/CCC/DDD/*

Select all elements enclosed by elements /AAA/CCC/DDD


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/*/*/*/BBB

Select all elements BBB which have 3 ancestors


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//*

Select all elements

Further conditions inside []

Expresion in square brackets can further specify an element. A number in the brackets gives theposition of the element in the selected set. The function last() selects the last element in the

selection.

/AAA/BBB[1]


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Select the first BBB child of element AAA

/AAA/BBB[last()]

Select the last BBB child of element AAA

Attributes

Attributes are specified by @ prefix.

//@id

Select all attributes @id

//BBB[@id]

Select BBB elements which have attribute id


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//BBB[@name]

Select BBB elements which have attribute name

//BBB[@*]

Select BBB elements which have any attribute

//BBB[not(@*)]

Select BBB elements without an attribute

Attribute values

Values of attributes can be used as selection criteria. Function normalize-space removes leading

and trailing spaces and replaces sequences of whitespace characters by a single space.

//BBB[@id='b1']

Select BBB elements which have attribute id with value b1


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//BBB[@name='bbb']

Select BBB elements which have attribute name with value 'bbb'

//BBB[normalize-space(@name)='bbb']

Select BBB elements which have attribute name with value bbb, leading and trailing spaces are

removed before comparison

Nodes counting

Function count() counts the number of selected elements

//*[count(BBB)=2]

Select elements which have two children BBB


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//*[count(*)=2]

Select elements which have 2 children

//*[count(*)=3]

Select elements which have 3 children

Playing with names of selected elements


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Function name() returns name of the element, the starts-with function returns true if the first

argument string starts with the second argument string, and the contains function returns true ifthe first argument string contains the second argument string.

//*[name()='BBB']Select all elements with name BBB, equivalent with //BBB

//*[starts-with(name(),'B')]

Select all elements name of which starts with letter B

//*[contains(name(),'C')]


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//*[string-length(name()) > 3]Select elements with name longer than three characters

Combining XPaths with |

Several paths can be combined with | separator.

//CCC | //BBB

Select all elements CCC and BBB

/AAA/EEE | //BBB

Select all elements BBB and elements EEE which are children of root element AAA


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/AAA/EEE | //DDD/CCC | /AAA | //BBB

Number of combinations is not restricted

Child axis

The child axis contains the children of the context node. The child axis is the default axis and it

can be omitted.

/AAA

Equivalent of /child::AAA

/child::AAA

Equivalent of /AAA

/AAA/BBB

Equivalent of /child::AAA/child::BBB


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/child::AAA/child::BBB

Equivalent of /AAA/BBB

/child::AAA/BBB

Both possibilities can be combined

Descendant axis

The descendant axis contains the descendants of the context node; a descendant is a child or a

child of a child and so on; thus the descendant axis never contains attribute or namespace nodes

/descendant::*

Select all descendants of document root and therefore all elements


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/AAA/BBB/descendant::*Select all descendants of /AAA/BBB

//CCC/descendant::*

Select all elements which have CCC among its ancestors


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//CCC/descendant::DDD

Select elements DDD which have CCC among its ancestors

Parent axis

The parent axis contains the parent of the context node, if there is one.

//DDD/parent::*

Select all parents of DDD element


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Ancestor axis

The ancestor axis contains the ancestors of the context node; the ancestors of the context nodeconsist of the parent of context node and the parent's parent and so on; thus, the ancestor axis

will always include the root node, unless the context node is the root node.

/AAA/BBB/DDD/CCC/EEE/ancestor::*

Select all elements given in this absolute path

//FFF/ancestor::*


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Select ancestors of FFF element

Following-sibling axis

The following-sibling axis contains all the following siblings of the context node.

/AAA/BBB/following-sibling::*


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//CCC/following-sibling::*

Preceding-sibling axis

The preceding-sibling axis contains all the preceding siblings of the context node

/AAA/XXX/preceding-sibling::*


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//CCC/preceding-sibling::*

Following axis

The following axis contains all nodes in the same document as the context node that are after thecontext node in document order, excluding any descendants and excluding attribute nodes and

namespace nodes.

/AAA/XXX/following::*


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Preceding axis

The preceding axis contains all nodes in the same document as the context node that are beforethe context node in document order, excluding any ancestors and excluding attribute nodes and

namespace nodes

/AAA/XXX/preceding::*


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Descendant-or-self axis

The descendant-or-self axis contains the context node and the descendants of the context node

/AAA/XXX/descendant-or-self::*


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Ancestor-or-self axis

The ancestor-or-self axis contains the context node and the ancestors of the context node; thus,the ancestor-or-self axis will always include the root node.

/AAA/XXX/DDD/EEE/ancestor-or-self::*

Orthogonal axes

The ancestor, descendant, following, preceding and self axes partition a document (ignoring

attribute and namespace nodes): they do not overlap and together they contain all the nodes inthe document.


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//GGG/ancestor::*

Numeric operations

The div operator performs floating-point division, the mod operator returns the remainder from atruncating division. The floor function returns the largest (closest to positive infinity) number

that is not greater than the argument and that is an integer.The ceiling function returns thesmallest (closest to negative infinity) number that is not less than the argument and that is an

integer.

//BBB[position() mod 2 = 0 ]

Select even BBB elements


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//BBB[ position() = floor(last() div 2 + 0.5) or position() = ceiling(last() div 2 + 0.5) ]

Select middle BBB element(s)

//CCC[ position() = floor(last() div 2 + 0.5) or position() = ceiling(last() div 2 + 0.5) ]Select middle CCC element(s)

Xpath Notes

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