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5. FDs and BCNF (Formal) > EXERCISES
5.1 The version of join defined in the body of the chapter is an n-adic operator, not just a dyadic one. But what happens if n = 1? Or n = 0?
5.2 Define as precisely as you can what it means for a relvar to be subject to a functional dependency.
5.3 Consider the following FDs:
-
{ CITY } ? { STATUS } -
{ SNO , CITY } ? { STATUS } -
{ SNO } ? { SNO } -
{ SNO , CITY } ? { SNO } -
{ SNO } ? { SNO , CITY } -
{ SNAME , SNO } ? { STATUS , CITY } -
{ SNO } ? { STATUS } -
{ SNAME } ? { STATUS , SNO }
Which of these FDs are trivial? Which ones are satisfied by the current value of relvar S as given in Figure 1-1? Which hold in relvar S? Which are irreducible with respect to relvar S?
5.4 Prove Heath’s Theorem. Prove also that the converse of that theorem isn’t valid. Note: In this connection, see also Exercise 11.3 in Chapter 11.
