Common Methods to Override

FormDataObject.Modified

Use this method when the user changes the contents of the field. This event can
be used to make calculations or other operations which depend on the field.
For system-wide functionality during a manual change of a database field,
override the modifiedField method on the table.

FormDataObject.Validate

Use this method to validate the contents of the field. This event can be used to
supplement or remove the ordinary validation.
For system-wide functionality during the validation of a database field,
implement this by overriding the validateField method on the table. 

Best Regards,
Hossein Karimi