Information Modeling and Relational Databases, 2nd Edition

14.4. Other Transformations

The previous two sections covered the most useful conceptual schema transformations. In this section, several other transformations of lesser importance are considered briefly.

Recall PSG2, our second predicate specialization/generalization theorem (Figure 14.16). This may be generalized further by removing constraints. First note that removing the UC on A’s role in R corresponds to removing the UC’s on A’s roles in each of the S_i predicates (see Figure 14.36). In the absence of additional internal UCs, the R and S_i binaries will be many:many. As an example, let A = Car, B - Status {’company’, ‘private’}, C = Employee, T = has, R = is used by, S_i = is provided for, and S₂ = is privately used by. Allow the same employee ...