What happens in the execution of a BPMN process, when an activity is reached that is marked with a small plus-symbol (+)? The plus-symbol indicates that the activity has another, detailed BPMN model attached. When the activity is reached, the process engine starts executing the attached model. When this detailed process is finished, the execution of the main process continues.
BPMN distinguishes between „real“ subprocesses and call activities. A subprocess is part of the top level process and can directly access its data. A call activity, on the other hand, calls a separate process. Therefore it is necessary to specify the data to be transferred to this process, as well as the data to be returned to the top level process.
Other than subprocesses, independent processes can be called by different call activities in different processes. Therefore it is possible to re-use processes with the help of call activities.
Since call activities are more flexible, some BPM systems don’t support subprocesses as a separate concept. The example in the video also contains a call activity.