@abc.abstractmethod<EOL><INDENT>def get_root_banks(self):<DEDENT>
return<EOL>
Gets the root banks in this bank hierarchy.

        :return: the root banks
        :rtype: ``osid.assessment.BankList``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure occurred

        *compliance: mandatory -- This method is must be implemented.*