1️⃣ High-Level Overview
| Aspect | IDoc (Intermediate Document) | API (REST / OData / SOAP) |
|---|---|---|
| Integration Style | Message-based, asynchronous | Service-based, synchronous or asynchronous |
| Technology | ALE / EDI | REST, OData, SOAP |
| Usage Era | Legacy + still supported | Strategic, future-ready |
| S/4HANA Strategy | Supported but not preferred | Recommended by SAP |
2️⃣ Architecture & Data Flow
| Area | IDoc | API |
|---|---|---|
| Trigger | Event-driven or batch | Real-time request/response |
| Payload | Fixed structure segments | Flexible JSON/XML |
| Processing | Background processing | Immediate processing |
| Error Feedback | Delayed (status records) | Instant HTTP response |
👉 Interview insight:
SAP promotes “API-first” in S/4HANA, but IDocs still exist for backward compatibility.
3️⃣ Development & Flexibility
| Area | IDoc | API |
|---|---|---|
| Customization | Requires extension (WE30) | Extend via CDS / BAdIs |
| Versioning | Difficult | Easy & controlled |
| Reusability | Low | High |
| Learning Curve | Steep | Easier for cloud integrations |
4️⃣ Performance & Scalability
| Area | IDoc | API |
|---|---|---|
| Throughput | High volume batch | Optimized real-time |
| Latency | High | Low |
| Scalability | Limited | Cloud-scalable |
| Monitoring | WE02 / BD87 | API logs / CPI / CIG |
5️⃣ Error Handling & Monitoring
| Area | IDoc | API |
|---|---|---|
| Error Detection | Status codes (51, 64) | HTTP status (4xx, 5xx) |
| Reprocessing | Manual (BD87) | Automated retries |
| Debugging | WE19, WE02 | API trace, CPI logs |
6️⃣ Security
| Area | IDoc | API |
|---|---|---|
| Authentication | RFC / Port-based | OAuth 2.0 / Certificates |
| Encryption | Limited | HTTPS / TLS |
| Compliance | Basic | Enterprise-grade |
7️⃣ S/4HANA + Ariba Context (Very Important for Interviews)
📌 SAP Ariba Integration Reality
| Scenario | Preferred Method |
|---|---|
| S/4HANA → Ariba (P2P) | CIG + APIs |
| Legacy ECC → Ariba | IDocs |
| Supplier invoices | APIs |
| Master data replication | APIs / CDS |
| Custom legacy interfaces | IDocs (if unavoidable) |
👉 Golden Interview Line:
“In S/4HANA, APIs are the strategic choice, while IDocs are supported mainly for legacy and transition scenarios.”
8️⃣ When Should You Use What?
✅ Use IDocs when:
- Migrating from ECC to S/4HANA
- High-volume batch processing
- Legacy third-party systems
- No API available
✅ Use APIs when:
- Cloud-to-cloud integration
- SAP Ariba, CPI, CIG
- Real-time transactions
- Clean Core strategy
9️⃣ Common Interview Questions & Smart Answers
Q: Are IDocs obsolete in S/4HANA?
➡️ No. They are supported but SAP recommends APIs for new developments.
Q: Can APIs replace IDocs completely?
➡️ Functionally yes, but practically IDocs remain for legacy compatibility.
Q: What does SAP recommend for Ariba integration with S/4HANA?
➡️ CIG with APIs.
🔟 One-Line Summary for Interviews
IDocs = Legacy, batch, robust
APIs = Future, real-time, cloud-ready
Coming up with more Ariba Interview Prep Content. Do follow up for more.