What is the purpose of a Sequence Diagram in describing system interactions? When is it needed?

Sequence Diagram is used to visualize interactions between objects or systems over time. It shows the order of messages and calls, helping to understand how components exchange data and respond to each other.

When needed:

• When designing new systems or modules to clarify interaction logic.
• For analyzing and documenting existing processes.
• When identifying bottlenecks or errors in communication between components.
• To align requirements among business analysts, developers, and testers.

Example: if you need to show how a user initiates a request through an interface, which passes through several services and returns a result, the Sequence Diagram visually displays this message flow over time.