Choosing an XPath conditional expression that tests for a nil value in a transform

Use the XPath functions fn:empty, fn:nilled, or fn:exists to test if an output element is set to nil. You can use these functions to define conditional expressions in a transform.

About this task

For example, you can use fn:empty, fn:nilled, or fn:exists as part of conditional expression that determines if a transform is applied. You can also use these transforms as part of the conditional expressions that you set in an IF transform.

Procedure

Choose any of the following XPath functions to determine the state of a source element:

XPath function	Usage	Source element	Output
fn:empty	Tests whether a set of elements is empty	A single XML or non-XML element that is present and nilled	false
fn:empty	Tests whether a set of elements is empty	A NULL value in a logical tree	false
fn:empty	Tests whether a set of elements is empty	A missing element, not present in the logical tree	true
fn:nilled	Tests whether an element is nilled	A nillable XML element	true only if the xsi:nil attribute is present and set to 'true' in the logical tree
fn:nilled	Tests whether an element is nilled	A nillable non-XML element	true only if the value in the logical tree is NULL
fn:exists	Tests whether an element exists	A single XML or non-XML element	true if the element is present in the logical tree, regardless of the nillable and nilled state
fn:exists	Tests whether an element exists	A NULL value in a logical tree	true
fn:exists	Tests whether an element exists	A missing element, not present in the logical tree	false

Example

This example shows an XPath expression that checks if an input element is nilled.

The XPath expression evaluates to true when an input element is not set to nil.

Use the fn:nilled XPath function to test whether the value of an input element has the xsi:nil attribute set.

Note: An XML element that has the xsi:nil attribute set is considered to be present.

The XML schema for the element is the following:

<element name="BookName" type="string" nillable="true" ></element>

The XPath expression that you define is the following:

fn:nilled( $BookName)