Process Interactions - Involving Externals


After completing this lesson, you will be able to Ask the right questions to obtain relevant process information.

Process Interaction and Collaboration

External Participants

External participants can be perfectly modeled with a collapsed pool - and hence be considered as a black box. The interaction with such "externals" can only be represented by message flows, which always indicate an exchange of information.


Sequence flows can never cross the border of a pool - but message flows can.

Usage of Message Flows

Message flows are used for communication between pools only. They are not used for internal communication as we have the sequence flow for this occasion. The other way around we cannot use sequence flows to communicate with other pools but rather use message flows.

Business Example - Let's Apply What You've Learned

Order Management

This example shows a more realistic example of how to interact with external participants and contains different elements that you have already learned in the course:

  • External participants and interaction.
  • Expanded subprocess for summarizing task.
  • with a cancel condition.
  • Collapsed subprocess - and evaluating the result.
  • Attached intermediate event (here: conditional event).
  • Starting message events.
  • Usage of IT-systems (spoiler: next lesson).

Using these different elements allows us to model an easy-to-follow order management process, which has some exceptional conditions with a loop in it.

Process Collaboration (Correspondence Diagrams)

The supreme discipline in process modeling is to model different processes and their interactions. However, there are some considerations as this is not always useful and can easily lead to problems and the entire process model can no longer be understood by others.

We only recommend modeling different processes in one model, when:

  • it is important to show interaction on task level.
  • the processes are not too complex.
  • it is still "easy to follow" and not too overloaded.

Example: Process Collaboration (Correspondence Diagrams)


If you use this way of process communication, remember that both pools are self-contained and have their independent processes - including their individual goals.

Key Takeaways - Process Collaboration and Interaction

Congratulations. You've completed the Process Interactions - Involving Externals lesson. Now, let's look at IT Systems and Data Object usage.

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