Subprocesses
Subprocesses are processes that exist within another process.
Note: A subprocess has access to all variables in all its parent processes (including parent subprocesses).
Subprocesses are of two types, standard and event-based.
Standard Subprocess
A standard subprocess can only be reached by a sequence flow in the parent process.
A standard subprocess can begin with a unique empty Start Event, or an activity or gateway that has no incoming sequence flow. It cannot start with a message, signal, or timer start event.