Linking to the Enterprise Model
The reader should have already figured out that Case looks suspiciously like Project from the Activity model in Chapter 7. Indeed, it is a logical sub-type of Project, as shown in Figure 18-4. This means, among other things, that the relationship from Case to Activity is, in fact, a sub-type of the relationship between Project and Activity.
Figure 18-4: Linking to the Enterprise Model
The constraint that asserted that “each Activity must be part of either one Case or one other Activity actually was inherited (via the sub-type relationship) from the assertion that each Activity must be either part of one Project ...