Include and extend dialog box

Inclusion and extension relationships between use cases

If you want a use case to use a functionality provided by another use case, you can create an «include» relationship between the two use cases. In this case, the behavior of the included use case is inserted into the behavior of the including use case. A use case can be included by one or more other use cases, thereby helping to reduce duplication of functionality by factoring out common behavior into use cases that are re-used many times.

The behavior of a use case can be extended by the behavior of another use case using the «extend» relationship. Extension takes place at one or more specific extensions points defined in the extended use case.

Inclusion and extension relationships both use the "extend" dialog box.

The "Properties" tab of the "extend" dialog box

The "Properties" tab of the "extend" dialog box is used to define the values of an inclusion or extension relationship.

The "Properties" tab of the "extend" dialog box

Key:

· "Use case source": This indicates the use case that is going to extend or include the other use case (indicated in the "Use case destination" field). You can drag and drop a use case into this field from the explorer or a diagram.

· "Use case destination": This indicates the base use case that is going to be extended or included by the use case indicated in the "Use case source" field. You can drag and drop a use case into this field from the explorer or a diagram.

· "Extension points": This window shows the extension points that exist in the base use case (indicated in the "Use case destination" field). To select all the extension points in the list, click on the button. To unselect all the extension points in the list, click on the button. To move a selected extension point up or down in the list, use the and buttons respectively.