Association Relationships

An association is a structural relationship showing that objects of one classifier (actor, use case, class, interface, node, or component) are connected and can navigate to objects of another classifier. An association connects two classifiers—supplier classifier consumer classifier—even in bi-navigable associations. Associations help you make design decisions about the structure of your data—not only the classes needed to contain the data, but also which classes need to share data with other classes. An association supports data sharing between classes or, in the case of a self-association, between objects of the same class.

For example, in an e-commerce application, a "Customer" class may have a single association (1) to an "Account" class, indicating that each "Account" instance is owned by one "Customer" instance. Also, if you have an "Account," you can locate its owning "Customer." Furthermore, with a given "Customer," you can navigate to each "Account." The association between the "Customer" class and the "Account" class is important because it shows the structure between each classifier.

An association end contains the properties that specify how one classifier structurally relates to the other classifier in the association. Both ends of an association can connect to the same class to show a self-association, indicating that given an object of this class, you can navigate to other objects of the same class.

Association appearance and semantics are determined by the properties of the association and its ends. The toolbox contains several associations tools with predefined properties. After an association is created, you can modify its appearance and semantics by changing its properties in the Properties window.

A bi-navigable association appears as a solid line between two classifiers.

You can name an association to describe the nature of the relationship between the two classifiers; however, names are typically not needed, especially if you use association end names.

• Directed Association Relationships
• Specifying Kinds of Association Relationships
• Specifying Navigability in Association Ends
• Specifying Visibility in Association Ends
• Relationships and Connectors

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