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)
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