BusinessRules in CAF field validation

In the Form, i want to validate CAF fields using business rules. I understand the ways to invoke IS service in CAF or work with business rules separately.

How to make the rule validate the inputs given in my fields? should the validate done in decision tables work fine when i invoke the same IS service in CAF?

Thanks for your inputs !

Have you thought about writing a server-side validator that invokes the IS Service? I think that is probably the approach that i would explore first.
Regards, --mark