@abc.abstractmethod<EOL><INDENT>def get_hierarchy(self, hierarchy_id):<DEDENT>
return<EOL>
Gets the ``Hierarchy`` specified by its ``Id``.

        In plenary mode, the exact ``Id`` is found or a ``NotFound``
        results. Otherwise, the returned ``Hierarchy`` may have a
        different ``Id`` than requested, such as the case where a
        duplicate ``Id`` was assigned to a ``Hierarchy`` and retained
        for compati

        :param hierarchy_id: the ``Id`` of the ``Hierarchy`` to retrieve
        :type hierarchy_id: ``osid.id.Id``
        :return: the returned ``Hierarchy``
        :rtype: ``osid.hierarchy.Hierarchy``
        :raise: ``NotFound`` -- no ``Hierarchy`` found with the given ``Id``
        :raise: ``NullArgument`` -- ``hierarchy_id`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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