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Complete Diagram Guide

by Peta Team

Complete Diagram Guide

Introduction
Flowchart Diagrams
Gantt Charts
Sequence Diagrams
Class Diagrams
State Diagrams
Advanced Features
Best Practices

Sequence Diagrams

Sequence diagrams visualize interactions between different actors or components over time. They're perfect for showing how systems communicate, API flows, and process interactions.

Basic Syntax

The fundamental syntax for sequence diagrams shows messages passing between actors:

Basic Sequence Actor A Actor B Message

This creates a simple interaction between two actors.

Message Syntax

Sending Messages

Messages are defined using arrow syntax:

RST 

1
2   Actor A -> Actor B: Message content

Components:

  • Source: The actor sending the message
  • Arrow: `->` indicates a message
  • Destination: The actor receiving the message
  • Message: Description of the message (optional)

Example:

Message Exchange User System Login Request Login Response

Creating Actors

Actor Creation

Actors are automatically created when they first appear in the diagram. You don't need to declare them explicitly.

Alice Bob Hello Hi there!

Multiple Actors

Use as many actors as needed:

Multi-Actor Interaction User Frontend API Database Request Call Query Data Response Result

Message Flows

Linear Flow

Sequential messages:

A B C D Message 1 Message 2 Message 3

Request-Response Pattern

Show request-response pairs:

Request-Response Client Server Request Response

Complex Interactions

Multiple Exchanges

Show back-and-forth communication:

Multiple Exchanges User App Auth Database Login Validate Success Fetch Data Data Welcome

Branching Logic

Represent conditional flows:

Conditional Flow User System Validator Processor Action Check Valid Execute Done Success

Practical Examples

User Authentication

User Authentication Flow User Login Page Auth Service Database Session Service Submit Credentials Validate Query User User Data Valid Create Session Session ID Redirect to Dashboard

E-commerce Checkout

E-commerce Checkout Customer Cart Inventory Checkout Payment Bank Order Email Add Item Check Stock Available Update Total Proceed Process Charge Confirmed Success Create Send Confirmation Receipt

API Request Handling

API Request Flow Client API Gateway Auth Load Balancer Service Cache Database GET /resource Validate Token Valid Forward Request Check Cache Cache Miss Query Data Store Response Response JSON Response

Tips and Best Practices

  1. Clear actor names: Use descriptive, concise names
  2. Logical flow: Arrange messages in chronological order
  3. Meaningful messages: Describe what each message represents
  4. Consistent direction: Show time flowing downward
  5. Appropriate detail: Include relevant steps without overwhelming

Common Patterns

Error Handling

Error Handling Client Service Validator Request Validate Error Error Response

Parallel Processing

Parallel Requests Client Service A Service B Request 1 Request 2 Response 1 Response 2

Data Synchronization

Data Sync Source Sync Service Validator Target Send Data Validate Valid Forward Data Acknowledge Confirm

Next Steps

Now that you understand sequence diagrams, let's explore class diagrams for visualizing system architecture in the next chapter.