The extending use case is dependent on the extended (base) use case.

Here are a few things to consider when using the << extend > relationship.

As the name implies it extends the base use case and adds more functionality to the system. An extend flow points toward the Use Case that is extended. Extend Relationship Between Two Use Cases Many people confuse the extend relationship in use cases. From the Use Case scenarios you can generate Activity diagrams, Sequence diagrams and StateMachine diagrams as starting points for the analytical modeling. Extend Flow - indicates that a Use Case extends the activity of another. The main connectors that can appear in Use Case diagrams are:Ī Use Case diagram can be used to define the details of a Use Case and its Scenarios and Constraints, with tight connectivity and traceability, as the Use Case diagram and the textual details of the Use Cases, Scenarios and Constraints are all contained in the same model. The main elements that can appear in Use Case diagrams are: Using the Scenario builder, behavioral model diagrams can then be generated from these text-based details to provide a base for the more detailed design. Each Use Case can be detailed, with descriptions, constraints and any number of scenarios that contain sets of steps performed alternately by Actor and system to achieve the desired goal.Ī core aspect of modeling Use Cases is performed using the Use Case Scenario feature, which helps add a more detailed text-based representation of the underlying Use Case. While the Use Case diagram can appear simplistic, it is a powerful communication device that describes the value or goals that external roles achieve from interacting with the system. (All elements are internal to the SysML diagram frame.) Enclosing the Use Case within a Boundary defines the border of the system the Actors by definition lie outside the boundary. The Use Case diagram describes the relationship between the Actors and the Use Cases. Use Case DiagramĪ SysML Use Case diagram is used to define and view Use Cases and the Actors that derive value from the system. Use Cases also support more detailed definition via Use Case Scenarios.

Describe the manner in which outside things (Actors) interact at the system boundary.

Expand on (or 'realize') the functional requirements of the system.

Use Case diagrams capture Use Cases and the relationships between Actors and the subject (system). Use Cases are intended to provide a more detailed expression of the requirements modeled on a higher level. The SysML notation for a Use Case is an ellipse, as for the UML notation. The arrow of an Extend Notation should point to the extended use case.Īn Extend Notation should also be labeled with the '>' key word.įor example, the 'On-Line Help' use case is an extension to the 'Place Order' use case.A Use Case represents a single unit of meaningful work, providing a high-level view of behavior observable to someone or something outside the system.

The add-on use case is usually called the Extending Use Case.Īn Extend Notation is usually drawn as a dash line with a line arrow connecting both use cases. The base use case is usually called the Extended Use Case.

An Extend Notation presents an extension relation between two use cases where one acts as the base use case and the other acts as an add-on use case.Īn Extend Notation is a graphical notation used in a UML Use Case Diagram to representĪn extension relation between two use cases where one acts as the base use case and the other acts as an add-on use case. This section describes the Extend Notation used in a UML Use Case Diagram. UML Tutorials - Herong's Tutorial Examples

Extend in use case diagrams