Sainath,
PI can be used to just handle the file exchange if you want to do all mapping in ERP.
Ideally Ariba ITK is the best solution for this requirement.
When the ABAP program provided by Ariba is scheduled to run in SAP, it downloads master and transaction status data from the SAP R/3 system to the configured location on your file system. The data is downloaded in the form of CSV files.
The Data Transfer Tool downloads transactional data from Ariba procurement solutions to the configured location on your file system. The data from Ariba procurement solutions is exported in the form of CSV files that are generated for each integration event that you run.
Basically PI can just do this CSV file exchanges between ERP and Ariba Network using File/SFTP adapters.
Discuss the possibility of using Ariba Integration Content and Ariba adapters which is the right approach with PI.
regards,
Arun