I have some question about XPDL specification:

1) Reading the XPDL 2.1a specification is not clear which are the differences between a receive task and the message event. I have read that the receive task is specialised for web service calls and the message event is more generic.

2) In a package there can be more than one pool and these can communicate together.
In the execution phase, one process model can have more than one process instances so when one process instance has to communicate (with message flow) with another process how can it decide with which process instance have to communicate?

3) A Event raised is visible in the context where it was raised or everywhere (for each active process instances)?

Thanks, Nunzio

The receiveTask and messageEvent are very similar in functionality and in some way redundant. Visually there are some useful distinctions because the receiveTask activity can have boundary events. So for instance if you want the task to terminate with an exception flow, a timerEvent on the boundary will do the trick. With a messageEvent you would use an event-based gateway followed by the messageEvent and the timerEvent. In BPMN2 Finalization Task Force there is some discussion about deprecating receiveTask and sendTask but no decision yet.

Correlation keys are used to distinguish between process instances. The subFlow element has an attribute used for this purpose:
InstanceDataField The name of the DataField in which to store the subflow instance id for subsequent use such as messaging or correlation. Typically used with ASYNCHR execution.

Please rephrase your 3rd question about 'Event raised is visible in the context'.

Thanks for the answer.

I try to rephrase the 3rd question: a Event thrown in a process instance can be catched only from a catch type Event in the same process instance?

Thanks