Message (Sequence Diagram)


Sequence diagrams depict work flow or activity over time using Messages passed from element to element. These Messages correspond in the software model to Class operations and behavior.

How to:

To create a Message on a Sequence diagram, follow the steps below:



See Also


Access the Sequence diagram

The Interaction pages of the Toolbox display.



In the Interaction Relationships page, click on the Message icon, click on the source object and drag the cursor to the destination (target) object

The Message Properties dialog displays (if not, right-click on the Message and select the Message Properties context menu option)



In the Message field, type the Message name:

  • If the Message flow is towards a Class element (dropped in from a Class diagram) or a Lifeline element having a classifier, and the destination Class has defined operations, you can click on the drop-down arrow and select an appropriate operation name; the Message then reflects the destination Class operations
  • If the available operations are not appropriate, you can click on the Operations button and define a new operation in the target element, using the Operations dialog
  • If you create a Message without making reference to the target Class operations, no new operation is added to the target Class

Class Element


Operations Dialog


In the Parameters field, type any parameters that the Message has, as a comma-separated list

If required, in the Parameter Values field type the actual value for each parameter, again as a comma-separated list



If the Message is a return message, in the Return Value field enter the returned value or type

It is possible to depict returns from a Self Message; simply create a second Self Message at the end of execution and select the Is Return checkbox in the Control Flow Type panel



If the Message flow is from a Class element or Lifeline element with classifier that has defined attributes, click on the drop-down arrow in the Assign to field and select an appropriate attribute name

The Message reflects the attributes from the source Class; you cannot add further attributes to the source Class here - if no appropriate attribute is listed, open the element Properties dialog and add the required attribute

Otherwise, if required, type the name of the object to assign the message flow to



In the Stereotype field, type or select an optional stereotype for the connector (this is displayed on the diagram, if entered)



If required, in the Alias field type an alias for the name of the Message

On the diagram, the alias displays if the Use Alias if Available checkbox is selected on the Diagram tab of the Diagram Properties dialog

The Alias displays instead of or as well as the Message name, depending on the setting selected in the Alias Usage panel of the Diagram Behavior page of the Options dialog

Diagram Behavior Options


In the Condition field, type any conditions that must be true in order for the message to be sent



In the Synch: field in the Control Flow Type panel, select Synchronous or Asynchronous as appropriate

Asynchronous Signal Message


In the Lifecycle field, select New to create a new element at the end of the Message, or Delete to terminate the message flow at the end of the Message

If neither case applies, leave the field at the default of <none>



If required, in the Notes field type any explanatory notes

You can format the notes using the Notes toolbar at the top of the field



Click on the OK button to save the Message definition

  • You can change the timing details of a message on the Timing Details dialog, and emphasize the sequence of closely-ordered messages using General Ordering
  • To toggle the numbering of messages on a Sequence diagram, select or deselect the Show Sequence Numbering checkbox on the Options dialog

Change the Timing Details

General Ordering

Sequence diagrams

Toolbox Icon:


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