Sending a Message to an Interaction Participant

Information exchange takes place by way of messages that are sent from the sender to the receiver and which contain the information to be transmitted.

Context

In order to express that a message is being sent, in UML sequence diagrams a signal is sent from the sender to the receiver, i.e. from one lifeline to another. The signal includes the information to be transmitted.

How to proceed

Left-click to select the vertical (dashed) part of the lifeline from which the message should be sent.

The selected lifeline is outlined with a blue frame and the carousel appears.
Move the mouse pointer over the Off Signal... connection type.
To create a message flow to an existing lifeline, drag the link to it with the mouse button pressed and release the mouse button.

The Requirement dialog opens and includes the signals already defined in your model.
Select an existing signal or use the Create new element button to create a signal which has not yet been defined. In the latter case, a wizard will then take you through the necessary steps.
Confirm your selection with OK.

The message edge is created and labeled with the name of the signal sent.