code: def rdb_repository(_context, name=None, make_default=False,
                     aggregate_class=None, repository_class=None,
                     db_string=None, metadata_factory=None):
      
      cnf = {}
      if not db_string is None:
          cnf['db_string'] = db_string
      if not metadata_factory is None:
          cnf['metadata_factory'] = metadata_factory
      _repository(_context, name, make_default,
                  aggregate_class, repository_class,
                  REPOSITORY_TYPES.RDB, 'add_rdb_repository', cnf)
docs: Directive for registering a RDBM based repository.