BPMN2.0 Messages vs DataObjects

[Mr Stuff]

Messages only flow between Pools, but when there is a choice, when should one use message flows and when should one pass dataobjects directly or via Data Stores?

And then, when dataobjects are appropriate, how can dataobject elements be reused when a) the same type of object appears in multiple processes and b) when the same object appears more than once in a process? (The two cases of, dataobject-has-state and dataobject-does-not-have-state can be considered separately).

Thanks, Julian
EA V12.1 Corporate Edition