Creating messages in sequence diagrams

A message represents an interaction between objects, or between an object and the environment. A message can be an event, a triggered operation, or a primitive operation. In the metamodel, a message defines a specific type of communication. The communication can be raising a signal, starting an operation, or creating or destroying an instance.

About this task

The recipient of a message is either a class or a reactive class. Reactive classes have statecharts, whereas nonreactive classes do not. Reactive classes can receive events, triggered operations, and primitive operations. Non-reactive classes can receive only messages that are calls to primitive operations. Events are typically shown with slanted arrows to imply that they are asynchronous (delivery takes time). Triggered operations are shown with straight arrows to imply that they are synchronous (happen immediately).

Procedure

  1. Depending on what type of message you want, click the Message button Message button has full arrowhead or the Event button Event button has thin arrowhead.
    Note: Use the Message button for messages for operations. By default, the product creates a primitive operation with public access. Use the Event button for messages for events. Notice the different arrowheads for the different message types.
  2. Move the cursor over the instance lines.
    Note: A plus sign displays on each instance line as you move the cursor from one to the next. This symbol indicates a potential origination point for the wanted message.
  3. Right-click to anchor the start of the message at the intended location, then move the cursor. A dashed line displays as a guide for the message.
  4. Move the cursor lower the start of the message to create a downward-slanted diagonal line and click the target object line to anchor the end of the message.
  5. If you specified design mode, and the specified message is not realized in the model, the product asks if you want to realize it. Click OK.

Results

The product creates a message with the default name message_n(), where n is an incremental integer starting with 0. Sequence diagrams automatically expand in length to accommodate new messages. To set or change the features for a message, double-click it to open its Features window.


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