XPath uses path expressions to select nodes or node-sets in an XML document. The node is selected by following a path or steps.
The XML Example Document
We will use the following XML document in the examples below.
<?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>
|
Selecting Nodes
XPath uses path expressions to select nodes in an XML document. The node is selected by following a path or steps. The most useful path expressions are listed below:
| Expression | Description |
| nodename | Selects all child nodes of the node |
| / | Selects from the root node |
| // | Selects nodes in the document from the current node that match the selection no matter where they are |
| . | Selects the current node |
| .. | Selects the parent of the current node |
| @ | Selects attributes |
Examples
In the table below we have listed some path expressions and the result of the expressions:
| Path Expression | Result |
| bookstore | Selects all the child nodes of the bookstore element |
| /bookstore | Selects the root element bookstore
Note: If the path starts with a slash ( / ) it always represents an absolute path to an element! |
| bookstore/book | Selects all book elements that are children of bookstore |
| //book | Selects all book elements no matter where they are in the document |
| bookstore//book | Selects all book elements that are descendant of the bookstore element, no matter where they are under the bookstore element |
| //@lang | Selects all attributes that are named lang |
Predicates
Predicates are used to find a specific node or a node that contains a specific value.
Predicates are always embedded in square brackets.
Examples
In the table below we have listed some path expressions with predicates and the result of the expressions:
| Path Expression | Result |
| /bookstore/book[1] | Selects the first book element that is the child of the bookstore element |
| /bookstore/book[last()] | Selects the last book element that is the child of the bookstore element |
| /bookstore/book[last()-1] | Selects the last but one book element that is the child of the bookstore element |
| /bookstore/book[position()<3] | Selects the first two book elements that are children of the bookstore element |
| //title[@lang] | Selects all the title elements that have an attribute named lang |
| //title[@lang='eng'] | Selects all the title elements that have an attribute named lang with a value of 'eng' |
| /bookstore/book[price>35.00] | Selects all the book elements of the bookstore element that have a price element with a value greater than 35.00 |
| /bookstore/book[price>35.00]/title | Selects all the title elements of the book elements of the bookstore element that have a price element with a value greater than 35.00 |
Selecting Unknown Nodes
XPath wildcards can be used to select unknown XML elements.
| Wildcard | Description |
| * | Matches any element node |
| @* | Matches any attribute node |
| node() | Matches any node of any kind |
Examples
In the table below we have listed some path expressions and the result of the expressions:
| Path Expression | Result |
| /bookstore/* | Selects all the child nodes of the bookstore element |
| //* | Selects all elements in the document |
| //title[@*] | Selects all title elements which have any attribute |
Selecting Several Paths
By using the | operator in an XPath expression you can select several paths.
Examples
In the table below we have listed some path expressions and the result of the expressions:
| Path Expression | Result |
| //book/title | //book/price | Selects all the title AND price elements of all book elements |
| //title | //price | Selects all the title AND price elements in the document |
| /bookstore/book/title | //price | Selects all the title elements of the book element of the bookstore element AND all the price elements in the document |
The XML Example Document
We will use the following XML document in the examples below.
<?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>
|
XPath Axes
An axis defines a node-set relative to the current node.
| AxisName | Result |
| ancestor | Selects all ancestors (parent, grandparent, etc.) of the current node |
| ancestor-or-self | Selects all ancestors (parent, grandparent, etc.) of the current node and the current node itself |
| attribute | Selects all attributes of the current node |
| child | Selects all children of the current node |
| descendant | Selects all descendants (children, grandchildren, etc.) of the current node |
| descendant-or-self | Selects all descendants (children, grandchildren, etc.) of the current node and the current node itself |
| following | Selects everything in the document after the closing tag of the current node |
| following-sibling | Selects all siblings after the current node |
| namespace | Selects all namespace nodes of the current node |
| parent | Selects the parent of the current node |
| preceding | Selects everything in the document that is before the start tag of the current node |
| preceding-sibling | Selects all siblings before the current node |
| self | Selects the current node |
Location Path Expression
A location path can be absolute or relative.
An absolute location path starts with a slash ( / ) and a relative location path does not. In both cases the location path consists of one or more steps, each separated by a slash:
An absolute location path: /step/step/... A relative location path: step/step/... |
Each step is evaluated against the nodes in the current node-set.
A step consists of:
- an axis (defines the tree-relationship between the selected nodes and the current node)
- a node-test (identifies a node within an axis)
- zero or more predicates (to further refine the selected node-set)
The syntax for a location step is:
axisname::nodetest[predicate] |
Examples
| Example | Result |
| child::book | Selects all book nodes that are children of the current node |
| attribute::lang | Selects the lang attribute of the current node |
| child::* | Selects all children of the current node |
| attribute::* | Selects all attributes of the current node |
| child::text() | Selects all text child nodes of the current node |
| child::node() | Selects all child nodes of the current node |
| descendant::book | Selects all book descendants of the current node |
| ancestor::book | Selects all book ancestors of the current node |
| ancestor-or-self::book | Selects all book ancestors of the current node - and the current as well if it is a book node |
| child::*/child::price | Selects all price grandchildren of the current node |
An XPath expression returns either a node-set, a string, a Boolean, or a number.
XPath Operators
Below is a list of the operators that can be used in XPath expressions:
| Operator | Description | Example | Return value |
| | | Computes two node-sets | //book | //cd | Returns a node-set with all 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 | true if price is 9.80 false if price is 9.90 |
| != | Not equal | price!=9.80 | true if price is 9.90 false if price is 9.80 |
| < | Less than | price<9.80 | true if price is 9.00 false if price is 9.80 |
| <= | Less than or equal to | price<=9.80 | true if price is 9.00 false if price is 9.90 |
| > | Greater than | price>9.80 | true if price is 9.90 false if price is 9.80 |
| >= | Greater than or equal to | price>=9.80 | true if price is 9.90 false if price is 9.70 |
| or | or | price=9.80 or price=9.70 | true if price is 9.80 false if price is 9.50 |
| and | and | price>9.00 and price<9.90 | true if price is 9.80 false if price is 8.50 |
| mod | Modulus (division remainder) | 5 mod 2 | 1 |
The following reference library defines the functions required for XPath 2.0, XQuery 1.0 and XSLT 2.0.
Functions Reference
The default prefix for the function namespace is fn:, and the URI is:
http://www.w3.org/2005/02/xpath-functions.
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