The model shown in Figure 1.6 below (about publishers and books) serves as our running example for a unidirectional functional association. Notice that it contains the unidirectional many-to-one association Book-has-Publisher.

Figure 1.6. The Publisher-Book information design model with a unidirectional association

We may also have to deal with a non-functional (multi-valued) reference property representing a unidirectional non-functional association. For instance, the unidirectional many-to-many association between Book and Author shown in Figure 1.7 below, models a multi-valued (non-functional) reference property authors.

Figure 1.7. The Publisher-Book-Author information design model with two unidirectional associations