Hi Nandu,
Another approach would be more robust and comparatively easy to be build.
PR created in Ariba with "DPAS_Rated" flag set to 'false' by default-> Approvals in Ariba -> PR post approvals sent to ECC as a PR -> DPAS Rating obtained for PR in ECC -> DPAS Rated PR exported from ECC via IDOC/SOAP/WSDL to Ariba (standard Req Import) -> All Req import set as auto approved in Ariba -> PO sent to Ariba Network.
The only problem with this approach is that for every purchase request there will be two PR#'s generated in Ariba so few more customizations to handle user notification and correct reporting should be done.
Regards
Vilas