Validation in Module Pool Program

Hi,

I have created a MP prog to update table 'x'.

Now the fields of table 'x' r coming from other tables. say 'y' and 'z'.

I have to validate those fields against their respective helps.

I have provided f4 help also.

But i m facing problem during validation.

I have tried function 'F4IF_FIELD_VALUE_REQUEST' also.

Regards,

Chaitanya