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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_root_objective_bank_ids(self, alias):
 """Gets the root objective bank Ids in this hierarchy. return: (osid.id.IdList) - the root objective bank Ids raise: OperationFailed - unable to complete request raise: PermissionDenied - authorization failure compliance: mandatory - This method must be implemented. """

        url_path = self._urls.roots(alias)
        return self._get_request(url_path)