Call activities are used to start an instance of another process definition. The original process waits until the called process is complete before continuing with its own process flow.
The calledElement property uses a processDefinitionId to define which process to start.
Note:
When a call activity element is executed it receives its own processInstanceId. The process variables of a call activity are also completely separate to those in the parent process.
Note:
Call activities can only be used to start a process instance of a process definition that exists in the same application as the process that is calling it.