diff --git a/SDT/schema4.0/test/subdevices-test.xml b/SDT/schema4.0/test/subdevices-test.xml
new file mode 100644
index 0000000000000000000000000000000000000000..7487a3a26587250030cbc662a190d0c7dc171bfb
--- /dev/null
+++ b/SDT/schema4.0/test/subdevices-test.xml
@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="iso-8859-1"?>
+<!-- Test the sub-device references -->
+
+<Domain id="subdevices-test" xmlns="http://www.onem2m.org/xml/sdt/4.0" xmlns:xi="http://www.w3.org/2001/XInclude">
+	<SubDevices>
+		<SubDevice id="aSubDevice">
+			<ModuleClasses>
+				<ModuleClass name="aModuleClass">
+					<Data>
+						<DataPoint name="aDataPoint">
+							<DataType>
+								<SimpleType type="boolean" />
+							</DataType>
+						</DataPoint>
+					</Data>
+				</ModuleClass>
+			</ModuleClasses>
+		</SubDevice>
+	</SubDevices>
+
+	<DeviceClasses>
+		<DeviceClass id="aDeviceClass">
+			<SubDevices>
+				<SubDevice id="subDevice">
+					<Extend domain="subdevices-test" entity="aSubDevice" />
+				</SubDevice>
+			</SubDevices>
+		</DeviceClass>
+	</DeviceClasses>
+</Domain>
\ No newline at end of file