How and where to validate datefield value on form.

Hi,

I have scenario where i have 2 datasources on single form

Some controls has datsource = DS1

Grid das datasource = DS2

when user enter enters values for controls for datasource1, how/where can i validate whether user has entered values for controls/grid for 2nd datsource as well.

DS1 and DS2 has relation.

How and where (which method) can be used to validate same?

Thanks,

Ragards,

Rahul$