Sequence Diagram

One of four types of Interaction diagram. (The other three are Timing Diagrams, Interaction Overview Diagrams and Communication Diagrams.)

A Sequence diagram is a structured representation of behavior as a series of sequential steps over time. It is used to depict work flow, message passing and how elements in general cooperate over time to achieve a result.

• Each sequence element is arranged in a horizontal sequence, with messages passing back and forward between elements.
• 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 configure a Sequence diagram, see the following topics:

• Denote the Lifecycle of an Element
• Layout of Sequence Diagrams
• Sequence Element Activation
• Lifeline Activation Levels
• Message Label Visibility
• Change the Top Margin
• Change the Timing Details

Robustness diagrams, used extensively in the ICONIX Process, can be created as Sequence diagrams.

Example Diagram

The following example Sequence diagram demonstrates several different elements:

Toolbox Elements and Connectors

Select Sequence diagram elements and connectors from the Interaction pages of the Enterprise Architect UML Toolbox.

Enterprise Architect also supports a number of stereotyped elements to represent various entities in business modeling.

OMG UML Specification

The OMG UML specification (UML Superstructure Specification, v2.1.1, p. 503) states:

A sequence diagram describes an Interaction by focusing on the sequence of Messages that are exchanged, along with their corresponding OccurrenceSpecifications on the Lifelines.