The XPath expression uses a path notation like URLs, for addressing parts of an XML document. The expression is evaluated to yield an object of the node-set, Boolean, number, or string type. For example, the expression book/author will return a node-set of the <author> elements contained in the <book> elements, if such elements are declared in the source XML document.
In XPath, path expression is used to select nodes or node-sets in an XML document. The node is selected by following a path or steps.
Let's take an example to see the syntax of XPath. Here, we take an XML document.
<?xml version="1.0" encoding="UTF-8"?> <bookstore> <book> <title lang="en">Three Mistakes of My Life</title> <price>110</price> </book> <book> <title lang="en">Immortals of Meluha</title> <price>200</price> </book> </bookstore>
Path expressions used for selecting nodes are:
| Index | Expression | Description |
|---|---|---|
| 1) | nodename | Selects all nodes with the name "nodename" |
| 2) | / | Selects from the root node. |
| 3) | // | Selects nodes in the document from the current node that match the selection no matter where they are. |
| 4) | . | Selects the current node |
| 5) | .. | Selects the parent of the current node |
| 6) | @ | Selects attributes |
See the path expressions and their details in the above example:
| Path Expression | Result |
|---|---|
| bookstore | Selects all nodes with the name "bookstore" |
| /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 are used to find a specific node or a node that contains a specific value.
Predicates are always embedded in square brackets.
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. Note: In IE 5,6,7,8,9 first node is[0], but according to W3C, it is [1]. To solve this problem in IE, set the selectionlanguage to XPath: in JavaScript: xml.setProperty("SelectionLanguage","XPath"); |
| /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='en'] | Selects all the title elements that have a "lang" attribute with a value of "en". |
| /bookstore/book[price>100] | Selects all the book elements of the bookstore element that have a price element with a value greater than 100 |
| /bookstore/book[price>100]/title | Selects all the title elements of the book elements of the bookstore element that have a price element with a value greater than 100 |
XPath wildcards are used to select unknown XML nodes.
| Wildcard | Description |
|---|---|
| * | Matches any element node |
| @* | Matches any attribute node |
| node() | Matches any node of any kind |
See this in above example:
| Path Expression | Result |
|---|---|
| /bookstore/* | Selects all the child element nodes of the bookstore element |
| //* | Selects all elements in the document |
| //title[@*] | Selects all title elements which have at least one attribute of any kind |
The | operator is used in XPath expression to select several paths. From the above example, we have listed some path expressions and 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 |
