RAP defines the architecture for OData services based on CDS semantic data models and ABAP behavior---this is the current model.

The predecessor is the ABAP Programming Model for SAP Fiori (BOPF/CDS-based), which can be migrated into RAP; it also exposes ABAP backend logic via CDS semantics.

ABAP Cloud Development Model (B) is the rule set/contract (release contracts, checks), not the service-building model. CAP (C) targets Node.js/Java on BTP, not ABAP-based backend services.