XML in a Nutshell, 3rd Edition

Name

xsi:nil

Synopsis

The xsi:nil attribute indicates that a certain element does not have a value or that the value is unknown. This is not the same as having a value that is zero or the empty string. Semantically, it is equivalent to SQL’s null. For example, in this full_name element, the last_name child has a nil value:

<full_name xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <first_name>Cher</first_name>
  <last_name xsi:nil="true"/>
</full_name>

It is not relevant whether an empty-element tag or a start-tag/end-tag pair is used to represent the nil element. However, a nil element may not have any content.

In order for this document to be valid, the element declaration for the name element must explicitly specify that nil values are allowed by setting the nillable attribute to true. For example:

<xs:element name="last_name" type="xs:string" nillable="true"/>