messages2.xml

<bpmn:collaboration id="my_collaboration">
    <bpmn:participant id="buddy" name="Buddy" processRef="process_buddy" />
    <bpmn:participant id="Person" name="Person" 
                      processRef="random_person_process" />
    <bpmn:messageFlow id="love_letter_flow" name="Love Letter Flow" 
            sourceRef="ActivitySendLetter" targetRef="Event_0ym6ptw" />
    <bpmn:messageFlow id="response_flow" name="response flow" 
            sourceRef="Activity_13eq2gr" targetRef="EventReceiveLetter" />
    <bpmn:correlationKey name="lover">            
        <bpmn:correlationPropertyRef>Lover_first_name</bpmn:correlationPropertyRef>      
        <bpmn:correlationPropertyRef>Lover_last_name</bpmn:correlationPropertyRef>
    </bpmn:correlationKey>
</bpmn:collaboration>