Another tactic we might consider for reducing redundancy in examples like that of Figure 15-7 is to introduce some relation valued attributes or RVAs. Figure 15-9 below gives an example. However, one obvious problem with this approach—quite apart from all of the usual problems that always attend the use of RVAs—is again asymmetry: On what basis do we decide to use an RVA for tutors and not for students or courses? And in any case, does this tactic really reduce redundancy? Again I’ll come back to this question later, in the section MANAGING REDUNDANCY.

Figure 15-9. Using an RVA for tutors