BPMN Combining Collaboration Diagrams or using Call Activity

Question

Let's say I have a collaboration diagram that models a process named CheckMessage which is quite complex and spans over few lanes and pools. Now I would like to model another process, e.g. CreateMessage which would make use of the previous process to check first if message doesn't exist already or if all its fields are valid, etc.

The thing is, that both processes make use of the same swimlanes and pools. What is the proper way to model such interactions? I was thinking to model CheckMessage as a sub-process of CreateMessage, however sub-processes can't be attached to pools or lanes - if I understand it correctly they just stay within a lane of activity which invoked them. Can a Call Activity encapsulate such beahviour (cross pools and lanes)? Or can I somehow reference the CheckMessage diagram as a whole?

Thanks in advance.

Answer 1

I could think of the following approaches:

1. Using Diagram Reference: This is used quite often when you want to switch easily to the more complex part. The disadvantage is that, unlike Fragments in SDs, you do not have ways to really connect flows in and out of referenced diagrams.
2. Repeating parts of the process: here you just pick those actions from the complex process which ought to interact with the other process. You can highlight that by putting a boundary around these and adding a diagram reference as described above.
3. Call Activity: This is another valid way. Here you have an activity which you instantiate as action. The advantage here is that you can add pins for input and output parameters.

I guess there is no silver bullet and you have to choose what is appropriate in each case.

Edit Regarding #3 it looks like that:

(this is an example and not to be used in practice) The Action to the right is an instance of the Activity as you can see by Ctrl-L (show parent).