I am new in the BPMN field and I have a question regarding the use of sequence flows and message flows. Here is an example of a collaboration between 2 pools.

Simple Collaboration Process

I wondere whether I should add a sequence flow between task A and Task B or not.

Could you please let me know what you think as well as explaining me the reason of your choice? I took a look at the specification but I did not find any clear explanation for such an example.

Thanks in advance



by Stefan Tilchner
Posted on Wed, 12/12/2012 - 05:28


in my opinion you need a sequence flow or an associated start event, as 'Task B' cannot be triggered otherwise. To be activated, it needs a token and this token has to come from 'Task A' or be generated somewhere else. So i see 2 possibilities: 

1. Add the sequence flow from 'Task A' to 'Task B' and make 'Task B' a receive task. This would trigger 'Task B' as soon as 'Task A' was completed and a message from 'Task E' was received. Although this would mean, that 'Task B' doesn't do anything but waiting for that message.

2. Add a message start event, that catches the message from 'Task E' and has an outgoing sequence flow to 'Task B'. This will activate 'Task B' as soon as the message was received.

The same would have to be done for 'Task A' and 'Task D' if you want the same behaviour, as right now your model tells me, that 'Task D' starts as soon as 'Pool B' starts and during execution, 'Task D' receives message(s) from 'Task A'. But it doesn't get activated by these messages.


Best regards,



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