code: def start_dag(self, dag, *, data=None):
          
          return self._client.send(
              Request(
                  action='start_dag',
                  payload={'name': dag.name if isinstance(dag, Dag) else dag,
                           'data': data if isinstance(data, MultiTaskData) else None}
              )
          ).payload['dag_name']
docs: Schedule the execution of a dag by sending a signal to the workflow.
  
          Args:
              dag (Dag, str): The dag object or the name of the dag that should be started.
              data (MultiTaskData): The data that should be passed on to the new dag.
  
          Returns:
              str: The name of the successfully started dag.