RAP Basics Part 8: Service Definition, Service Binding and OData Exposure

📌 KEY POINTS
✅ Service definition = what is exposed (expose ZC_Travel as Travel); service binding = how (protocol and purpose).
✅ Binding types: OData V4 – UI, OData V2 – UI, OData V4 – Web API, OData V2 – Web API (plus InA/SQL for analytics).
✅ UI bindings carry UI annotations for Fiori Elements; Web API bindings are for machine consumers and ignore UI metadata.
✅ Publishing registers the service (on-premise: local publish in ADT or via /IWFND/V4_ADMIN for V4 service groups) — no SEGW, no /IWFND/MAINT_SERVICE for V4.
⚠️ Exposing the UI projection as the integration API ties partners to UI changes — use a separate API projection and binding.

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▶ WHERE WE ARE
Parts 2–7 built the BO. Now we make it reachable.

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▶ 1. SERVICE DEFINITION

• define service ZUI_TRAVEL { expose ZC_Travel as Travel; expose ZC_Booking as Booking; }
• Also expose value-help views used in the projection if needed.
• Aliases become entity set names in $metadata.

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▶ 2. SERVICE BINDING

• Created in ADT from the service definition; choose binding type.
• OData V4 – UI is the default for new Fiori Elements apps (draft works best with V4).
• OData V2 – UI only if the UI technology requires V2.
• Web API: for integration (CPI, external systems); no Fiori preview.

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▶ 3. PUBLISHING

• ADT: Publish button on the binding (on-premise: local service endpoint).
• Transport: the binding is transported; in each system it must be published (V4: /IWFND/V4_ADMIN service group, V2: /IWFND/MAINT_SERVICE).
• BTP ABAP Environment: publish and create a communication scenario/arrangement for Web APIs.

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▶ 4. PREVIEW AND TEST

• Preview button on an entity set in the binding opens a Fiori Elements app — no UI5 code.
• Check $metadata; test with Gateway client or Postman.

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▶ 5. API DESIGN

• One API projection (ZA_* or ZAPI_*) with stable field names, its own service definition and Web API binding.
• Version: new incompatible changes → new service version, not silent changes.

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▶ STEP BY STEP

1. Create service definition ZUI_TRAVEL exposing the projection views.
2. Create binding ZUI_TRAVEL_O4 (OData V4 – UI) and publish.
3. Open the Fiori Elements preview and test create/edit/actions.
4. For integration: create ZAPI_TRAVEL service definition + Web API binding.

✅ CHECKPOINT: the preview shows the list report and object page, and $metadata lists Travel and Booking.

A client exposed its RAP UI service directly to a logistics partner through CPI. Six months later a UI enhancement renamed two fields in the projection for better Fiori labels, and the partner interface failed overnight. The architect introduced a dedicated API projection (provider contract transactional_interface) with its own service definition and Web API binding, documented as a stable contract. From then on, UI changes happened freely in ZC_* views while ZA_* stayed unchanged; incompatible API changes went into a new service version.

• Using the UI service for integration partners, coupling them to UI changes.
• Forgetting to publish the binding in the target system after transport.
• Choosing OData V2 for new draft-enabled Fiori Elements apps without a reason.
• Not exposing value-help views, so value helps are empty in the app.
• Looking for the V4 service in /IWFND/MAINT_SERVICE instead of /IWFND/V4_ADMIN.

• Separate UI (ZUI_*) and API (ZAPI_*) service definitions and bindings.
• Default to OData V4 – UI for new Fiori Elements apps.
• Include publishing steps in the cutover/transport checklist.
• Use the Fiori Elements preview early to validate annotations.
• Version APIs explicitly; never silently change a released contract.

Questions: "Difference between service definition and service binding?", "Which binding type would you choose for a Fiori app and for an integration?", "How do you publish a V4 service on-premise?"
Strong answer: service definition lists the exposed projections; the binding chooses protocol and purpose (V4/V2, UI/Web API). OData V4 – UI for new Fiori Elements apps, Web API bindings on a separate API projection for integration. On-premise V4 services are published via ADT or /IWFND/V4_ADMIN service groups; the binding must be published in each system.