Look, Read, Understand, Apply


OOAD - Object Oriented Analysis and Design

Sequence Diagram

Sequence diagram

Sequence diagram is a UML diagram which shows the dynamic behavior of the system. It shows the sequence of interaction between objects, life of the objects. The order in which messages are exchanged between the objects are clearly seen in the sequence diagram. Sequence diagrams are used to understand users’ requirement from the new system. It is used to:

  • To show the details of a case case.
  • To know the methods of the objects
  • To model the logic of procedure, function

Symbols used in Sequence diagram

RectangleObject SymbolRepresents a class or object
Vertical rectangleActivation boxRepresents the time taken by object to complete a task
Sticky SymbolActor symbolShow entity with the system
small vertical rectangle with dashed vertical line beneath the rectangleLifeline symbolRepresents the passage of time
FrameUsed for loop or alternative conditionUsed to model loop construct or conditional statement
ArrowSynchronous message symbolUsed to show a message send from a sender
Arrow with dashed lineReturn message symbolshows the reply messages

Sequence Diagram for Searching book in Search Engine

Sequence Diagram for Issuing book from library