@abc.abstractmethod<EOL><INDENT>def get_hierarchies_by_query(self, hierarchy_query):<DEDENT>
return<EOL>
Gets a list of ``Hierarchy`` objects matching the given hierarchy query.

        :param hierarchy_query: the hierarchy query
        :type hierarchy_query: ``osid.hierarchy.HierarchyQuery``
        :return: the returned ``HierarchyList``
        :rtype: ``osid.hierarchy.HierarchyList``
        :raise: ``NullArgument`` -- ``hierarchy_query`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure
        :raise: ``Unsupported`` -- ``hierarchy_query`` is not of this service

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