>
>Wouldn't one, at some point, also include validation through
>the Valid() or RangeLow() method for negative values?
>
>
>yes, multiple checks are good, but for me best is:
>- to prevent invalid input values for reduce user input invalid messages
>- put check into the fields for check programmatic errors

You could, of course, always use a spinner control. Users don't actually have to use the up down arrows.

>A Eiffel approach for any value stored is good,
>but best of the best
>is define a strong variable data type,
>valid only into a specific data values domain.
>
>For example a string domain with a regular expression like data domain,
>when the program write a value on a string variable,
>it validate the value in the domain automatically.

Well, one can use table and field validation for this. However, I think that at some point we start to have to argue about where exactly the dividing line between business and data logic is.