A message is a communication between objects that conveys information with the expectation that action will ensue. The receipt of a message is one kind of event.
The message is drawn as a horizontal line from one object lifeline to another. The message may also be drawn from and to the same object, representing a message from an object to itself.
To numbering manually
1 Open the definition dialog of the message.
2 Go to the Symbol tab and add a number to the Number field. Click OK to close the dialog.
You may add numbers with decimal points (ie, 2.1.3.4.5). Characters (ie, a.b.c, or 1.a.2) are not allowed. When manually numbering messages, it is up to the user to intelligently add numbers that sequentially follow the chronological ordering of messages on the Sequence diagram.
To set auto-numbering on for the Sequence diagram
1 Select Tools > Preferences. In the Auto group of the Preferences dialog, toggle on Number.
2 Select a Message line on a Sequence diagram, and choose Format, Symbol Format, Symbol Style. In the Symbol Style dialog, select Auto Number in the Allow group.
System Architect will try to assign a sequence number depending on the immediately adjacent (vertically) message sequence numbers when messages are added or moved around.
If you have not created sequence numbers on a Sequence diagram, you may automatically create them by synchronizing the diagram with its partner collaboration diagram (see below), then re-synchronize the Collaboration diagram back with the Sequence diagram.
Synchronizing message numbers with collaboration diagram
If the messages on a Sequence diagram have not been assigned numbers, numbers are automatically created when synchronizing the Sequence diagram to a Collaboration diagram (select Draw > Synchronize Diagram). The logic that System Architect follows is that if it encounters no sequence number in the first Message line on the Sequence diagram, it assigns ordinal numbers to that and all ensuing messages on the diagram.
Naming Messages: Message Name and Method Name
As you add messages to a Sequence diagram, you specify the name of the message. You may open the definition of the line to specify the method that the message invokes (see below).
Changing the Name of a Message
To change the name of a message, simply open the Message's definition dialog and change the name in the Name field (to open the message's definition dialog, double-clickclick the message, or right‑click it and select Edit, or select Edit > Message/Stimulus from the toolbar). This will change the name of the message. It will also change the name of any message of the same name drawn between the same two objects on the diagram. To prevent this from happening, single out the message for rename, as described below.
Singling out a message for rename
Often in a Sequence diagram, users may draw multiple message lines between two objects, and give them no name (or the same name). A problem occurs if the user tries to rename one of these messages -- all other messages of the same (or no) name also get changed. You may avoid this problem by singling out a message for rename, as follows:
1 Right-click a selected message symbol and then click Symbol Rename.
2 Give the symbol a new name in the Name field and click OK. This will provide the message with a unique, new definition -- separating it from other messages of the same name on the diagram.
Specifying message synchronization type
You may specify the Message Synchronization Type of messages drawn between objects. The message will be drawn differently based on the synchronization type.
Invoking a method on the target object/class
When one object sends a message to another object, it is asking that second object to do something. It invokes a method of the target object. The target object instantiates methods of its class and superclasses. You may specify the method in the message’s definition dialog (see Invoking a method on target object).
To show or hide the method name, right-click the message, and then click Display Mode.
Using focus of control/activation bars
You may Focus of control (activation bar) rectangles, or activation bars, on an object lifeline to show the period during which the object is performing an action.
Adding a note to a message
To add a note to a message, open the message’s definition dialog, go to its Symbol tab, and add the note text in the Graphic Comment property. The note will appear on the diagram, attached to the message line via a dashed line. Right‑click the message and choose Display Mode to specify whether you want all Graphic Comments (notes) displayed on the diagram, or for just the selected symbol.