
You can use BPMN collaborative models to model the messages that occur between business processes or between different organizations. In BPMN diagrams, pools distinguish processes, and messages represent the information that moves from one process pool to another. Typically, BPMN models model a single process. However, a BPMN diagram can reference additional processes by using call activities.
In the following image, a collaboration BPMN diagram describes the process that occurs between the Bank and Customer participant or pool.

You can use BPMN in an organization to model internal processes. The level of detail that you include in a BPMN diagram depends on its purpose, and can be simple or complex. You can also use BPMN models to represent external processes and refine those processes in a service model to represent a service that the business provides.
You can use service models to refine BPMN models by using existing elements in the BPMN model to create capabilities, participants, and service interfaces. Service models provide more detail about the service that the business process provides. You can transform BPMN models into code that developers can use to create the services that you refined from the BPMN model.