Collaboration: Message Flow quantity limitation? Why?


I'm trying to represent a simple Collaboration diagram between a customer and a seller using "black box" concept.

First Message Flow (from Customer to Seller): ask for product

Second Message Flow (from Seller to Customer): product

Third Message Flow (from Customer to Seller): payment

However, Bizagi says the third Message Flow is an error with Message: "It cannot be more than one connector between the same two elements".

BPMN specification says nothing about it. So why is it considered an error?

Comments (1)


Dear MY,

Thank you for letting us know your questions. This form of modeling is considered an error in the Bizagi Modeler because the implementation of a model does not consider the "black box" concept for whole processes. You can still model your process as in the image you shared with us and save it as is, but we would recommend that you model the process differently. For instance, "ask for product," "receive product," and "make payment" are activities within a process, so they should be modeled using tasks rather than message flows between processes. Conversely, message flow connectors are used specifically for sending messages between two different agents involved in a process (for example, asking for product could be expanded into a sub process that includes messages between customer and company). The decision to make it a task or a sub process depends on the level of detail you want your model to have.

For more information on the topics of interaction between processes and message flows, you can read the following articles:

Let us know if you have further questions.

Best regards,

Laura G