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.
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.
Example: Usage of Message Flows - Select each example to find out which is correct.
Business Example - Let's Apply What You've Learned
The process above shows a more realistic example of how to interact with external participants and also contains different elements you learned already in the course:
- External participants & 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 all these different elements allows us, modeling an easy-to-follow order management process, which has even some exceptional condition with a loop in it.
Process Collaboration (Correspondence Diagrams)
The supreme discipline in process modeling is, to model different processes and their interaction. However, there are some considerations as this is not always useful and can easily lead to the problem, the entire process model cannot be understood any more by other people.
We would only recommend modeling different processes in one model, when:
- Interaction on task level is important to show
- The processes are not too complex
- It's still "easy to follow" and not too overloaded