XPath beginners are actually very simple

XPath is a language used to search for information in XML documents. XPath is used to navigate through elements and attributes in XML documents.

(My understanding: XPath is a path language used to find XML nodes, and a path string syntax)

XML instance document

We will use this XML document in the following example.

<? XML version = "1.0" encoding = "ISO-8859-1"?>

<Bookstore>

<Book>
<Title lang = "eng"> Harry Potter </title>
<Price> 29.99 </price>
</Book>

<Book>
<Title lang = "eng"> learning XML </title>
<Price> 39.95 </price>
</Book>

</Bookstore>

Select Node

XPath uses path expressions to select nodes in XML documents. Nodes are selected by following the path or step. The most useful path expressions are listed below:

Expression	Description
Nodename	Select all child nodes of the node.
/	Select from the root node.
//	Select the nodes in the document from the current node that matches the selected node, regardless of their location.
.	Select the current node.
..	Select the parent node of the current node.
@	Select attributes.

In the following table, we have listed some path expressions and expression results:

Path expression	Result
Bookstore	Select All subnodes of the bookstore element.
/Bookstore	Select the root element bookstore. Note: If the path starts with a forward slash (/), the path always represents the absolute path to an element!
Bookstore/book	Select all the book elements that belong to the sub-elements of bookstore.
// Book	Select All book child elements regardless of their location in the document.
Bookstore // book	Select all the book elements belonging to the descendant of the bookstore element, regardless of where they are located under the bookstore.
// @ Lang	Select all properties named Lang.

Predicates)

It is used to find a specific node or a node that contains a specified value.

The predicates are embedded in square brackets.

In the following table, we list some path expressions with predicates and the results of the expressions:

Path expression	Result
/Bookstore/book [1]	Select the first book element that belongs to the bookstore sub-element.
/Bookstore/book [last ()]	Select the last book element that belongs to the bookstore sub-element.
/Bookstore/book [last ()-1]	Select the penultimate book element that belongs to the bookstore sub-element.
/Bookstore/book [position () <3]	Select the first two bookstore sub-elements.
// Title [@ Lang]	Select all the title elements with the lang attribute.
// Title [@ lang = 'eng']	Select All title elements and these elements have the lang attribute whose value is Eng.
/Bookstore/book [price> 35.00]	Select all the book elements of the bookstore element, and the value of the price element must be greater than 35.00.
/Bookstore/book [price> 35.00]/Title	Select all the title elements of the book element in the bookstore element, and the value of the price element must be greater than 35.00.

Select unknown Node

The XPath wildcard can be used to select unknown XML elements.

Wildcard	Description
*	Match any element node.
@*	Match any attribute node.
Node ()	Match any type of nodes.

In the following table, we list some path expressions and the results of these expressions:

Path expression	Result
/Bookstore /*	Select all child elements of the bookstore element.
//*	Select all elements in the document.
// Title [@ *]	Select All title elements with attributes.

Select several paths

You can select several paths by using the "|" operator in the path expression.

In the following table, we list some path expressions and the results of these expressions:

 

Path expression	Result
// Book/Title | // book/price	Select all the title and price elements of the book element.
// Title | // price	Select all the title and price elements in the document.
/Bookstore/book/Title | // price	Select all the title elements of the book element that belongs to the bookstore element and all the price elements in the document.

 

 

XPath axis (axes)

The axis defines the node set relative to the current node.

Axis name	Result
Ancestor	Select all the ancestors of the current node (parent, grandfather, etc ).
Ancestor-or-self	Select all the ancestors of the current node (parent, grandfather, etc.) and the current node itself.
Attribute	Select all attributes of the current node.
Child	Select all child elements of the current node.
Descendant	Select all descendant elements (child, sun, etc.) of the current node ).
Descendant-or-self	Select all descendant elements (child, sun, etc.) of the current node and the current node itself.
Following	Select all nodes after the end label of the current node in the document.
Namespace	Select All namespace nodes of the current node.
Parent	Select the parent node of the current node.
Preceding	Select all nodes before the start label of the current node in the document.
Preceding-sibling	Select all peer nodes before the current node.
Self	Select the current node.

 

XPath Operators

Operators available in XPath expressions are listed below:

Operator	Description	Instance	Return Value
|	Calculate two node sets	// Book | // CD	Returns all node sets with book and CD elements.
+	Addition	6 + 4	10
-	Subtraction	6-4	2
*	Multiplication	6*4	24
Div	Division	8 Div 4	2
=	Equal	Price = 9.80	If the price is 9.80, true is returned. If the price is 9.90, false is returned.
! =	Not equal	Price! = 9.80	If the price is 9.90, true is returned. If the price is 9.80, false is returned.
<	Less	Price <1, 9.80	If the price is 9.00, true is returned. If the price is 9.90, false is returned.
<=	Less than or equal	Price <= 9.80	If the price is 9.00, true is returned. If the price is 9.90, false is returned.
>	Greater	Price> 9.80	If the price is 9.90, true is returned. If the price is 9.80, false is returned.
> =	Greater than or equal	Price >=9.80	If the price is 9.90, true is returned. If the price is 9.70, false is returned.
Or	Or	Price = 9.80 or price = 9.70	If the price is 9.80, true is returned. If the price is 9.50, false is returned.
And	And	Price> 9.00 and price <9.90	If the price is 9.80, true is returned. If the price is 8.50, false is returned.
MoD	Calculate the remainder of the Division	5 mod 2	1

XPath beginners are actually very simple