> The advantage of specifying a + and a - in the type interface is that
> the unit definition can then be specified as part of the type
> declaration itself. So you can do:
>
> CREATE TYPE ts_sec AS RANGE OVER timestamp (UNIT = '1s');
> CREATE TYPE ts_min AS RANGE OVER timestamp (UNIT = '1m');
>
> All of the stuff about defining + and - is hidden from the user - it's
> part of the type interface, which is pre-created.
>
The disadvantage is that it does not permit irregularly spaced units.
-Nathan