A sequence diagram shows the order of interactions between systems, modules, or users.

You use it to document or design communication flows — especially when it matters who does what and when.

In SAP, that usually means:

IDoc flows
API calls
RFC sequences
Middleware handshakes (PO / CPI / Gateway)

📌 When to Use Sequence Diagrams

Use Case	Why It Helps
Explaining integration logic	Makes system communication explicit
Designing API / IDoc flows	Clarifies sender, receiver, steps
Documenting middleware behavior	Shows what goes through PO/CPI
Debugging timing/order issues	Visualize async vs sync
Functional/technical handoff	Aligns expectations between teams

🧩 Sequence Diagram Notation (PlantUML)

Element	Syntax	Meaning
Participant	`participant "Name"`	Actor or system
Actor	`actor "User"`	External user (optional)
Message (→)	`A -> B : message`	Synchronous call
Async (→>)	`A ->> B : fire-and-forget`	Asynchronous call (IDoc, CPI)
Return (--)	`B --> A : response`	Response
Notes	`note right of A : comment`	Comments

✅ Example: Create Delivery via Fiori

plantuml
CopyEdit
@startuml
title Sequence Diagram — Delivery Creation Flow

actor "User"
participant "Fiori App"
participant "SAP Gateway"
participant "Backend (S/4HANA)"
participant "Database"

"User" -> "Fiori App" : Submit Delivery
"Fiori App" -> "SAP Gateway" : OData Request
"SAP Gateway" -> "Backend (S/4HANA)" : Call BAPI
"Backend (S/4HANA)" -> "Database" : Update Tables
"Backend (S/4HANA)" --> "SAP Gateway" : BAPI Response
"SAP Gateway" --> "Fiori App" : Success
"Fiori App" --> "User" : Confirmation

@enduml

This is simple, but powerful.

You can use it to explain almost any SAP process that crosses boundaries.

🛠 Real SAP Use: IDoc Outbound via PO

plantuml
CopyEdit
@startuml
title Sequence Diagram — IDoc via SAP PO

participant "S/4HANA"
participant "SAP PO"
participant "3rd-Party System"

"S/4HANA" ->> "SAP PO" : Send IDoc (ORDERS05)
"SAP PO" ->> "3rd-Party System" : Transformed XML
"3rd-Party System" --> "SAP PO" : 200 OK
"SAP PO" --> "S/4HANA" : Status Update (optional)

@enduml

Use ->> for asynchronous messages like IDocs or messages to CPI/PO.

⚙️ Rules Recap

Define each participant
Use arrows to show direction
Label messages (what is sent)
Use >> for async flows (IDoc, JMS)
Keep sequence logical (top-down)
Add only meaningful participants

🧠 Pro Tips

✅ Use real names from your landscape (not just "System A")

✅ Combine with notes to explain behavior

✅ Use this in technical specs or when aligning with middleware teams

✅ It helps when onboarding new devs or partners

✅ Summary

If you're working on SAP integration, sequence diagrams are essential.

They show who talks to whom, when, and with what. That’s all you need.

Use them for:

IDoc and API flows
Middleware handoffs
Process debugging
Technical communication

Next up:

👉 Visual SAP #5 — Class Diagrams for ABAP: Make Logic Visual and Sharable

We'll map objects, methods, relationships — and show how to visualize your Z-logic before coding.

Visual SAP with plantUML #4 Sequence Diagrams