Database Design II : Keys and Related Constraints
Like the concept of database design in general, the familiar concept of a key in the relational sense also involves a number of complications in the temporal context that don’t arise in the conventional (nontemporal) context. This state of affairs arises in part because of the redundancy and circumlocution problems, first discussed in Chapter 5, that can arise in the temporal context. This chapter proposes two new kinds of constraints, PACKED ON constraints and WHEN / THEN constraints, that can be used to help address such problems. Together, these constraints lead to a generalization of the familiar key notion, referred to in this book as “U_keys.”
redundancy problem; circumlocution ...