Currently, if users want to signal or abort a process instance, they have to either pass in a processInstanceId or a correleationKey through the Message Context (which can come from SOAP headers, for example), so that the same instance can be associated.

It would be nice if the correlationKey (which is a form of business data) could come from somewhere else. For example, somewhere in the payload (the content of the Message) or maybe even a different context property. We could allow the user to specify an MVEL expression on how to traverse to get the value, just like we do for globals/inputs/outputs/faults.