Return Message: It defines a particular communication between the lifelines of interaction that represent the flow of information from the receiver of the corresponding caller message.Call Message: It defines a particular communication between the lifelines of an interaction, which represents that the target lifeline has invoked an operation.

The core of the sequence diagram is formed by messages and lifelines.įollowing are types of messages enlisted below:

They are in the sequential order on the lifeline. The messages depict the interaction between the objects and are represented by arrows. It describes that time period in which an operation is performed by an element, such that the top and the bottom of the rectangle is associated with the initiation and the completion time, each respectively. It is represented by a thin rectangle on the lifeline. Several distinct roles can be played by an actor or vice versa. An actor may or may not represent a physical entity, but it purely depicts the role of an entity. It represents the role, which involves human users and external hardware or subjects. ActorĪ role played by an entity that interacts with the subject is called as an actor. It is positioned at the top of the diagram.

It either models generic interactions or some certain instances of interaction.Īn individual participant in the sequence diagram is represented by a lifeline.

To model interaction among objects inside a collaboration realizing a use case.

To model high-level interaction among active objects within a system.

It incorporates the iterations as well as branching.

In UML, the lifeline is represented by a vertical bar, whereas the message flow is represented by a vertical dotted line that extends across the bottom of the page. It portrays the communication between any two lifelines as a time-ordered sequence of events, such that these lifelines took part at the run time. It helps in envisioning several dynamic scenarios. The sequence diagram represents the flow of messages in the system and is also termed as an event diagram.

Draw system sequence diagram online