def persist_upstream_structure(self):
        """Persist json file with the upstream steps structure, that is step names and their connections."""
        persist_dir = os.path.join(self.experiment_directory, '{}_upstream_structure.json'.format(self.name))
        logger.info('Step {}, saving upstream pipeline structure to {}'.format(self.name, persist_dir))
        joblib.dump(self.upstream_structure, persist_dir)