Extract from Wikipedia:
"Open Catalog Interface (OCI) is an open and standardized catalog data interface for the exchange of catalog data records between SAP eProcurement systems (usually "SAP Enterprise Buyer Professional", EBP for short) and any other catalogs. The SAP user directly accesses the provider's current catalog data via the Internet using standard Internet protocols. A frequently used term for this interface is also "punchout", because the SAP user is forwarded by the SAP system to an external shop system (usually the company's supplier). The shopping basket of the SAP system is then enriched with the articles in it, with the purchase order. The ordering process of the external shop system, which is addressed via OCI, is greatly shortened, since neither address data nor shipping or payment methods have to be entered or selected here. Usually only the overview of the articles in the shopping cart is necessary, then the shop is left again to SAP and the shopping cart content of the ext. shop is transferred to the shopping cart of the SAP system. The advantage is that the purchase from the supplier (who usually provides the shop system) is immediately booked in SAP. Disadvantage is that the suppliers can change their prices arbitrarily in their Shop, without this by the client (the SAP uses) is noticed. When creating the OCI catalogue, this must be created as a framework agreement in SAP. However, there is usually no control or warning if the prices in the catalog differ from the prices in the framework contract."