South East Training - Business Process Modelling Toolkit

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Boundary Events

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  • A common use of intermediate events is to channel flow onto the exception path from the boundary of an activity or sub-process. We have seen the use of the boundary error event and the cancel event when we looked at transactional sub-processes.
  • Two additional boundary events are shown: the boundary message event that is listening for a signal from within the sub-process and the boundary timer event that will channel flow along the exception path if the sub-process does not complete within a given period of time.
  • In this diagram they are shown as interrupting boundary events, meaning the sub-process will be interrupted if the boundary event receives a signal.
  • BPMN also offers designers the use of non-interrupting boundary events that allow the sub-process to complete normally but initiate a parallel exception path. A typical use of this facility would be to inform a supervisor or customer that a process was running late. You would not want to interrupt the process but you would need to let others know what was happening.

Boundary Events - Examples

  • The first example shows the use of the interrupting message boundary event.
    • Here the process of preparing an order for shipment would be cancelled immediately if the customer choses to cancel the order while the sub-process was active.
    • An alternative would be to use a transactional sub-process with a cancel event at the boundary. Resetting the transaction would mean putting goods for shipment back into the stock.
    • If the customer, however, simply wanted to amend the delivery address, you would use a non-interrupting message boundary event that would allow the sub-process to complete normally while updating the delivery details
  • The second examples shows an interrupting timer boundary event.
    • Here, the HR receives a request for some training. The first option is to explore their internal capacity to meet this need. If they cannot do so within a week (one of their KPIs perhaps), they need to look elsewhere and commission an external trainer.


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