What is a sequence diagram (UML Sequence Diagram)?

A Sequence Diagram in UML is a type of interaction diagram that shows how objects or components of a system interact with each other over time.

It displays:

• Participants (objects, classes, roles) as vertical lines (lifelines).
• Messages (method calls, data transfers) as arrows between these lines, arranged along a timeline from top to bottom.

A sequence diagram helps understand the order of calls and message exchanges in a system's workflow, which is useful for analyzing behavior, designing, and documenting processes.

Example of use: describing the user authentication process, where the client sends a request, the server checks the data, and returns a response.