...Take an employment termination date in a personnel record. While the employee is still employed, the termination date should (I suppose) be null, but that doesn't mean it's unknown, it means that because it hasn't yet happened yet it doesn't exist at all!...
Which can be viewed as at the current point in time it is unknown. N'est pas?
Gaz
-- Stop your grinnin' and drop your linen...they're everywhere!!!