join 2 tables between 2 persistance schema

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Java

join 2 table between 2 persistance unit

 <persistence-unit name="oltpJPA">
        <class>entity.timetable</class>
        		<class>entity.facultyleave</class> 
        		<properties>
        			<property name="openjpa.jdbc.Schema" value="OLTP" />
        			<property name="openjpa.ConnectionDriverName"value="com.ibm.db2.jcc.DB2Driver"/>
        			<property name="openjpa.ConnectionURL" value="jdbc:db2://172.16.1.7:50000/OLTPDB:retrieveMessagesFromServerOnGetMessage=true;"/>
        			<property name="openjpa.ConnectionUserName" value="administrator"/>
        			<property name="openjpa.ConnectionPassword" value="server"/>
        		</properties>
        
        
        	</persistence-unit>
        	
        <persistence-unit name="oltpJPAabs">
        	
        	<class>property.Properties</class>
        		
        		<class>entity.StudentAbsenteseDate</class>
        		<class>entity.StudentAbsenteseLecture</class>
        	<properties>
        			<property name="openjpa.jdbc.Schema" value="OLTP" />
        			<property name="openjpa.ConnectionDriverName" value="com.ibm.db2.jcc.DB2Driver"/>
        			<property name="openjpa.ConnectionURL" value="jdbc:db2://172.16.1.9:50000/OLTPDB:retrieveMessagesFromServerOnGetMessage=true;"/>
        			<property name="openjpa.ConnectionUserName" value="administrator"/>
        			<property name="openjpa.ConnectionPassword" value="lenovo"/>
        		</properties>
        	</persistence-unit></persistence>

not able to manage the foreign key between **studentabsenteselecture and timetable**