What is a Sequence Diagram?

The following article describes briefly the main parts of an UML 2.0 sequence diagram.

What it is?

A sequence diagram describes how your system actually works. In more precise words it describes how the parts of your system interacts with each other via messages (events)

If you are doing a sequence diagram always keep in mind this: How my system is getting the work done?

Overview

A sequence diagram is composed by the following parts:

• Participants: the parts of your system that interact with each other.
• Time: the life time of the participant (doted line).
• Events: Any point of interaction where something occurs.
• Messages: Occurs when some participant decides to send something to other participant (arrows).
• Activation: When a participant sends a message it triggers a the receiving participant into doing something, this is represented as a bar that indicates that the participant is doing something.

The following image describes the parts of a sequence diagram:

Parts of a sequence diagram

Reference:

Miles, R. & Hamilto, K.(2006) Learning UML 2.0. O’Reilly Media, Inc.