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I would like to know what's the best way to model a  situation when both initiator and a receiver actors are involved in a Use case.

- initiator sends a request for contact exchange (the inititator has a contact on pending state)

- receiver approves the contact exchange (the receiver has a contact on active state)

- initiator receives a confirmation (the inititator has contact on active state)

My ideas would be:

-  state diagram for "Contact" object - but that will only reflect the changes only for one Actor.

- BPMN diagram to reflect the process flow for both Actors

Is this enough or there is another diagram I can use?

Also, these diagrams focus on the main scenario but the alternatives how should be described in a diagram?

Thanks!