Specifying a Node Test in the Location Path

A node test specifies the node type selected by the location step. Every axis (child, parent, attribute, and self) has a principal node type. For the attribute axis, the principal node type is <attribute>. For the parent, child, and self axes, the principal node type is <element>.

Note  The wildcard node test * (for example, child::*) is not supported.

Node Test: Example 1

The location path child::Customer selects <Customer> element children of the context node.

In the example, child is the axis and Customer is the node test. The principal node type for the child axis is <element>. Therefore, the node test is TRUE if the <Customer> node is an <element> node. If the context node has no <Customer> children, an empty set of nodes is returned.

Node Test: Example 2

The location path attribute::CustomerID selects CustomerID attribute of the context node.

In the example, attribute is the axis and CustomerID is the node test. The principal node type of the attribute axis is <attribute>. Therefore, the node test is TRUE if CustomerID is an <attribute> node. If the context node has no CustomerID, an empty set of nodes is returned.

Note  In this implementation of XPath, if a location step refers to an <element> or an <attribute> type that is not declared in the schema, an error is generated. This is different from the implementation of XPath in MSXML, which returns an empty node set.

Abbreviated Syntax for the Axes

The following abbreviated syntax for the location path is supported:

• attribute:: can be abbreviated to @.

  The location path Customer[@CustomerID="ALFKI"] is the same as child::Customer[attribute::CustomerID="ALFKI"].

• child:: can be omitted from a location step.

  Thus, child is the default axis. The location path Customer/Order is the same as child::Customer/child::Order.

• self::node() can be abbreviated to one period (.), and parent::node() can be abbreviated to two periods (..).