The XML Path Language (XPath) is an XSL sub-language designed to
uniquely identify or address parts of a source XML document. An XPath expression
can be used to search through an XML document, and extract information from
the nodes (any part of the document, such as an element or attribute) in it.
There are four different kinds of XPath expressions:
- Boolean
- An expression type with two possible values.
- Node set
- A collection of nodes that match an expression's criteria, usually derived
with a location path.
- Number
- A numeric value, useful for counting nodes and for performing simple arithmetic.
- String
- A fragment of text that can be from the input tree, processed or augmented
with general text.
An XPath expression returns a certain node set, which is a collection of
nodes. For example, if you tell XPath to look for any element with an id attribute,
there can be more than one. XPath returns a node set, which is a collection
of all the elements in the input document that have an id element.
This is a sample XPath expression:
/order/item/part-number
Which means "select any elements named part-number,
which are children of item elements, which are children
of order elements which are children of the document root.
You can create an XPath expression using the XPath Expression wizard. You
can launch the XPath Expression wizard in the following ways:
- From the pop-up menu of any select or match attributes
in an XSL file. Select the attribute, right-click it, and click XPath
Expression.
- From any of the XSL editor wizards in which you can specify an XPath expression
for a field value. In the appropriate wizard, click the XPath button.