IF parent_id_ IS DISTINCT FROM old_parent_id THEN

        DECLARE

            -- These include the parent itself

            old_ancestors integer[] := (

                SELECT array_agg(ancestor_id) FROM taxonlabel_relationship

                WHERE descendant_id = old_parent_id

            );

            new_ancestors integer[] := (

                SELECT array_agg(ancestor_id) FROM taxonlabel_relationship

                WHERE descendant_id = parent_id_

            );

            descendant_id_ taxonlabel_relationship.descendant_id%TYPE;

            ancestor_id_ taxonlabel_relationship.ancestor_id%TYPE;

        BEGIN

            FOR descendant_id_ IN -- also includes self

                SELECT descendant_id

                FROM taxonlabel_relationship

                WHERE ancestor_id = new.taxonlabel_id

            LOOP

                -- Delete old parent's ancestors

                DELETE FROM taxonlabel_relationship

                WHERE descendant_id = descendant_id_

                AND ancestor_id = ANY (old_ancestors)

                ;

                -- Add new parent's ancestors

                FOR ancestor_id_ IN

                    SELECT unnest(new_ancestors)

                LOOP

                    INSERT INTO taxonlabel_relationship

                    (descendant_id, ancestor_id)

                    SELECT descendant_id_, ancestor_id_

                    ;

                END LOOP;

            END LOOP;

        END;

    END IF;

    /* Note: We don't need an ON DELETE trigger to update the descendants'

    ancestors when a node is deleted, because the

    taxonlabel_relationship.ancestor_id foreign key is ON DELETE CASCADE. */