UML Sequence diagrams show object interactions within a time sequence. Their focus is on the interaction between objects and not the details of the internal states of the involved objects. Such a sequence is usually only a small, repeateble cut-out of the system process. Because of the explicit illustration of the timeline sequence diagrams are suitable for description of temporal succession. The lifelines have only a qualitative relevance. For quantitative statements you need annotations.
Sequence diagrams are suitable for the visualization of individual execution scenarios like business processes or common system processes. They are also helpful for the illustration of processes in existing systems, for testing and for reengineering.
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An object stands for an active component of the system. You can create such a structure element via drag'n'drop. Drag an existing agent from the repository and drop it on the sequence diagram opened in edit-mode. You can create a new one from the template, too. You can stretch the lifeline to a user-defined length. The destruction icon (cross on the end of the lifeline) for the object deletion can be deleted via the context menu. |
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Activation blocks identify the time sequences the object is active in the process. The position and the length can be defined freely by the user. |
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Communication between objects is visualized by arrows. The communication between objects can be
You'll find distinct templates for each of these communication types. You can create an arrow per drag'n'drop onto a sequence diagram in edit mode. Each arrow has a comment, useful to specify the kind of message. |
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When the sending or receiving object is irrelevant you can use the context menu to create:
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This structure element marks the creation of an object instance. |