What is a 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)


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.
Parts of a sequence diagram


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



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Eduardo Uriegas

Eduardo Uriegas

Passion for life, believe in the power of education, committed with human and economic development.