One element references another when an attribute of the referencing element has the same value as an attribute of the referenced element. For example, the application-ref element references an application that is deployed to its parent server element. The application-ref element’s ref attribute has the same value as the name attribute of an application element.
The referencing application-ref element might look like this:
The referenced application element might look like this:
<application name="MyServlet" location="myservletdir"/>