A sequence diagram is a form of communication diagram that illustrates how different actors and objects interact with each other or between themselves. The diagram represents these interactions as an exchange of messages between various entities and the type of exchange. Sequence diagrams also demonstrate the sequence of events that occur in a specific use case and the logic behind different operations and functions.

Elements of a sequence diagram

Various elements make up a sequence diagram. Let's discuss some of the essential elements of this diagram that appear most often.


In sequence diagrams, we write all entities horizontally. Each entity has a lifeline that represents its existence, i.e., when the entity is activated or deactivated. We illustrate this using a dotted line below the entity. We represent different objects, actors, entities, or boundaries in a system using lifelines, and they never overlap each other. The illustration below shows how to visualize a lifeline in UML. The horizontal boxes are used to denote the objects involved in the interaction.

Level up your interview prep. Join Educative to access 70+ hands-on prep courses.