After going through some information i got some idea of ARIBA to S4 intergration, but have few doubts:
1. Can S4hana on Premise be connected to ARIBA without CIG?. If yes, what would CIG add value in integration.
2. One of option to connect S4HANA to ARIBA directly, is this through configuration in both S4 & ARIBA? What are Disadvantages of this method.
3. Can only PI/PO be used to intergrate S4HANA TO ARIBA, if so what are Disadvantages of this method.
Any working link for these questions are welcome.
Find below my personal comments on your questions:
1) Yes, S/4HANA can connect with SAP Business Network (Ariba Network) as a Buyer without CIG, but it is not recommended because you will have to convert everything to cXML and post it to the SBN directly.
You will have to have super deep knowledge of the cXML structure and its processes; that said, it is super recommended customers to use the CIG as SAP takes care of the cXML and S/4HANA transformation.
2) As mentioned before, SBN only reads cXML and you need to think how your S/4HANA would be able to send it?
You can read about cXML at https://cxml.org/.
3) SBN can accept integration from any middleware capable to generate the cXML, but as mentioned before you will have to master the cXML and that will require tons of hours exploring something that has been already taken care of by the CIG connection.
CIG is here to stay as the main connectivity for buyers and suppliers, and buyers should use it; if you are having a brand new implementation, SAP would provide Buyers Integrators resources to assist the customer/partner during its implementation.