Referential-integrity constraints as defined in this chapter involve exactly two relations. Consider a database that includes the following relations:

salaried-worker (name, office, phone, salary)

hourly-worker (name, hourly-wage)

address (name, street, city)

Suppose that we wish to require that every name that appears in address appear in either salaried-worker or hourly-worker, but not necessarily in both.

a. Propose syntax for expressing such constraints.

b. Discuss the actions that the system must take to enforce a constraint of this form.