> I guess I was stuck on the true sense of an integral type where
> it must hold a valid integer (0 or otherwise). (I minored in
> mathematics and look where it got me!)

I know what you mean here. I have miles of trigger code setup to
force null string and number values back to blank and 0. The main
fields I dont force are foreign keys, dates and optional boolean
because NULL has real meaning an use. Occassionally there are some
other exceptions but not many.

Try not to think of key values as numbers (or strings where you use
strings). Think of them as their own data type with their own
requirements - the use of surrogate keys helps with this idea.

Date and timestamps make an interesting analogy. Underneath they
may be numbers, and in certain instances number operations apply,
but it is a mistake to forget that they are dates. Many client
based systems use an imaginary '0' point to identify an unassigned
date. IB/FB use NULL and this tends to be much more appropriate.

hth

--
Geoff Worboys
Telesis Computing