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Sequence Diagram

A Sequence diagram is a structured representation of behavior as a series of sequential steps over time.

Use To:

  • Depict work flow, message passing and how elements in general cooperate over time to achieve a result
  • Capture the flow of information and responsibility throughout the system, early in analysis; messages between elements eventually become method calls in the Class model
  • Make explanatory models for Use Case scenarios; by creating a Sequence diagram with an Actor and elements involved in the Use Case, you can model the sequence of steps the user and the system undertake to complete the required tasks


  • Each sequence element is arranged in a horizontal sequence, with messages passing back and forward between elements
  • Messages on a Sequence diagram can be of several types; the Messages can also be configured to reflect the operations and properties of the source and target elements (see the Notes in the Message topic)
  • An Actor element can be used to represent the user initiating the flow of events
  • Stereotyped elements, such as Boundary, Control and Entity, can be used to illustrate screens, controllers and database items, respectively
  • Each element has a dashed stem called a Lifeline, where that element exists and potentially takes part in the interactions

To toggle the numbering of messages on a Sequence diagram, select or deselect the Show Sequence Numbering checkbox on the Options dialog.

Example Diagram:     Example Sequence Diagram


Select Sequence diagram elements and connectors from the Interaction pages of the Toolbox. Click on the following elements and connectors for more information.

Sequence Diagram Elements

Sequence Diagram Connectors



















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