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LLDsystem_design~12 mins

Use case diagrams in LLD - Architecture Diagram

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System Overview - Use case diagrams

A use case diagram visually shows how users (actors) interact with a system. It helps understand what the system does from the user's point of view. Key requirements include identifying actors, their goals, and the system's main functions.

Architecture Diagram
          +---------------------+
          |      System         |
          |  +---------------+  |
          |  | Use Case 1    |  |
+------+  |  +---------------+  |  +--------+
|Actor1|--|->| Use Case 2    |<-|--|Actor2  |
+------+  |  +---------------+  |  +--------+
          +---------------------+
Components
Actor1
actor
Represents a user or external system interacting with the system
Actor2
actor
Another user or external system interacting with the system
Use Case 1
use_case
A specific function or goal the system provides for Actor1
Use Case 2
use_case
Another function or goal shared by Actor1 and Actor2
System
system_boundary
Defines the scope of the system and contains use cases
Request Flow - 4 Hops
Actor1 → Use Case 1
Actor2 → Use Case 2
Use Case 2 → Actor1
Use Case 2 → Actor2
Failure Scenario
Component Fails:System
Impact:Actors cannot perform use cases; system functions are unavailable
Mitigation:Define fallback processes or manual operations outside the system
Architecture Quiz - 3 Questions
Test your understanding
What does an actor represent in a use case diagram?
AA software module inside the system
BA user or external system interacting with the system
CA database storing system data
DA network device routing requests
Design Principle
Use case diagrams focus on user goals and system functions, helping clarify system scope and user interactions before detailed design.