
SAP NetWeaver user interfaces offers a set of back-end services and front-end services. To decouple your UI, you use OData services for ABAP-based back-end systems based on an OData channel that is part of SAP NetWeaver Gateway. To couple to a new UI technology, you use front-end services.
APIs are available on three different layers:
JavaScript services provide integration capabilities and simplify access to data from back-end systems
OData services are consumed by the front-end services and allow you to retrieve data from back-end systems using SAP NetWeaver Gateway.
ABAP APIs are consumed by the OData services mentioned above. You can use these APIs to create your own services for maximum flexibility.