Sequence Diagram

About

A Sequence Diagram in UML represents how objects interact in a particular sequence over time. It is primarily used to illustrate the flow of messages between different components in a system. This diagram is essential for understanding dynamic behavior and how different parts of a system communicate.

Refer to the official documentation for more details - https://plantuml.com/sequence-diagram

Key Elements

1. Actors & Objects

   • Represented as stick figures (Actors) or rectangles (Objects).

   • Actors interact with the system (e.g., User, External System).

2. Lifelines

   • Dashed vertical lines indicating the object's existence over time.

   • Shows how long an object is active in the sequence.

3. Messages

   • Arrows representing method calls, responses, and interactions.

   • Types:

     • Synchronous (-->) – Caller waits for a response.

     • Asynchronous (->) – Caller continues execution without waiting.

4. Activation Bars

   • Vertical rectangles on lifelines showing when an object is active/executing.

   • Indicate processing time for a message.

5. Return Messages

   • Dashed arrows (-->>) representing responses or results sent back.

6. Loops & Conditions

   • Used to model iterations or conditional logic (e.g., alt, loop).

7. Destroying Objects

   • Represented by ‘X’ at the bottom of a lifeline when an object is deleted.

1. Fund Transfer

This sequence diagram represents a user performing a fund transfer in a banking system.

• Actors (participant): Represent different entities in the system.

• Messages (->): Show interactions between entities.

• Alternative (alt ... else): Conditional logic for valid/invalid accounts.

• Self-calls (->): Represents internal method calls within the same participant.

@startuml
title Fund Transfer Process

participant User
participant "Bank API" as BankAPI
participant "Account Service" as AccountService
participant "Transaction Service" as TransactionService
participant "Notification Service" as NotificationService

User -> BankAPI: initiateTransfer(sender, receiver, amount)
BankAPI -> AccountService: validateAccounts(sender, receiver)
AccountService -> BankAPI: return validation result

alt if accounts are valid
    BankAPI -> TransactionService: processTransaction(sender, receiver, amount)
    TransactionService -> AccountService: debit(sender, amount)
    TransactionService -> AccountService: credit(receiver, amount)
    TransactionService -> BankAPI: transaction success

    BankAPI -> NotificationService: sendTransferNotification(sender, receiver)
    NotificationService -> User: notify transaction success
else if accounts are invalid
    BankAPI -> User: notify validation failure
end

@enduml