ALV grid validation

Hi,

I am using ALV class functions to display a table entry.Not just display the entry but I can also create/update record using ALV.now when I enter datas in a column in ALV i want that column to be checked against another table field. At the table level I can do foreign key and validate the entries but before updating in database I want the entries to be validated.Can anyone tell me how to achieve this?

Thanks

Suganya