Association

An association provides a pathway for communication between use cases and actors. Associations are the most general of all relationships and consequentially, the most semantically weak. If two objects are usually considered independently, the relationship is an association. The association name and its stereotype are typically verbs or verb phrases and are used to identify the type or purpose of the relationship.

There are two different types of associations connected with use-case diagrams: uni-directional and bi-directional.

Uni-directional association: By default, associations in use cases are uni-directional and drawn with a single arrow at one end of the association. The end with the arrow indicates who or what is receiving the communication.

Bi-directional association: To change the communication to be bi-directional, double-click the association to view the Association Specification. Click the appropriate Role A (or B) Detail tab, select the Navigable check box, and click Apply. You have now made the association bi-directional. The graphic changes from a line with an arrow at one end to a line with no arrow.

If you prefer, you can also customize the toolbox to include the bi-directional tool in the use-case toolbox. See Customizing the Toolbox on page 11 for information on adding or deleting diagram toolbox tools.