How do you save it? The UI shouldn't do it, but pass the data to a middle tier business object for validation. The valid data should then be passes to a data object that actually saves the data.

The UI should never directly access the data, but always call a business object, than then calls the data object.

I know it sounds like lots of overhead, but if you're going to do multi-tier design, this is the simple way of doing it.

>If we are using invoice table, do you I need business logic whenever I use the tables? For example I have saved the total of Invoice at the time of saving record, now I have to simply use it in all reports etc instead of calculating again and again.
>
>Please don't mind my question but I could not justified the use of middle tier.
>
>Regards,