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Sequence Element Activations

Sequence elements in a Sequence diagram have Activation rectangles drawn along their lifelines. These rectangles describe the time the element is active during the overall period of processing. This visual representation can be suppressed by right-clicking the Sequence diagram, and selecting 'Suppress Activations'.

In general, Enterprise Architect calculates the period of activation for you, but in some cases you might want to fine tune the rectangle length. There are several context menu options on a Sequence Message that you can use to accomplish this. To access the context menu, right-click on the message and select 'Activations'.

A more convenient way to change activation levels is directly on the diagram. Whenever appropriate, left arrows and/or right arrows display on specific connectors. In this diagram, see connector 1.3. Click on the arrow to raise or lower the activation level.

Context menu options

Option

Description

Start New Message Group

Starts off a new round of processing in the current diagram.

This enables you to describe more than one processing scenario in a single diagram.

Extend Source Activation Down

Forces an element to stay active beyond the normal processing period.

This could be used to express an element that continues its own processing concurrently with other processes.

Extend Source Activation Up

Forces an element's activation upwards.

End Source Activation

Truncates the activation of the source element after the current message.

This is useful for expressing an asynchronous message after which the source element becomes idle.

End Target Activation

Ends a Forced Activation started by the 'Extend Source Activation' options.

Raise Activation Level

Displays on the context menu only where its use is appropriate.

For example, after a self-message the next message starts by default at a lower activation level but the 'Raise Activation Level' command displays on the context menu to enable you to raise its level.

Lower Activation Level

Displays on the context menu only where its use is appropriate.

Branch With Previous Message

[This section describes a method of representing concurrent messages as defined in UML prior to UML 2.0, and supports models that might still apply it.

From UML 2.0 onwards, this notation has been replaced by Fragments. It is recommended that you consider upgrading your models to make use of Fragments and other more recent improvements in notation. ]

Having set out the Lifelines and Sequence Messages with the appropriate message grouping and activation levels, you might want to indicate that two messages in different Message Groups and at different Activation levels issuing from a Lifeline are branches, or executed concurrently. Consider this example:

Message 1.1 passes from Object 5 to Object 6, and then Message 1.2 passes to Object 7 and Message 2.1 passes back to Object 5. It appears that the Messages go in the sequence 1.1, 1.2 and then 2.1. However, you want to indicate that Message 2.1, whilst separate, is concurrent with Message 1.2.

In this case:

  • Right-click on the later Message (2.1) and select the option 'Branch with Previous Message'

The source anchor for Message 2.1 then becomes the same as the source for Message 1.2, the immediately previous message. They are separate but concurrent Messages from the same Lifeline.

If it later becomes unnecessary to show that the Messages are branches, right-click on the later message (2.1) and deselect the 'Branch with Previous Message' option.

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