+void ovsdb_datum_union(struct ovsdb_datum *,
+ const struct ovsdb_datum *,
+ const struct ovsdb_type *);
+void ovsdb_datum_subtract(struct ovsdb_datum *a,
+ const struct ovsdb_type *a_type,
+ const struct ovsdb_datum *b,
+ const struct ovsdb_type *b_type);
+