Can I have one XML Schema (XSD) include another XML-Schema?
There are two methods for this.
<xsd:include schemaLocation="pathToFile" />
should be used for including files of the same namespace.
<xsd:import namespace="namespace" schemaLocation="pathToFile" />
should be used for include files in a different namespace. Usually you will specify the namespace given as the targetNamespace of the imported schema.