Ariba 9r1 field value real-time validation using Webservice?

Hi,

I'm new to Ariba 9r1 and our project manager is asking if a real-time validation of a field value to SAP (Requisition) will be possible using WebService.

Does any one here calling WebService in Ariba 9r1? and how can it be done?

Any inputs will be very helpful to us.