Databases Reference
In-Depth Information
constraint; in the suppliers-and-parts database, for example, deleting a supplier can't be done if it causes the
pertinent foreign key constraint to be violated).
EXERCISES
10.1 The following questions are repeated from Chapter 1, but you should have a better chance of answering them
now (assuming you couldn't do so before, that is).
a.
(
Exercise 1.6
.) Is it true that every “all key” relvar is in 5NF?
b.
(
Exercise 1.7
.) Is it true that every binary relvar is in 5NF?
c.
(
Exercise 1.8
.) Is it true that if a relvar has just one key and just one other attribute, then it's in 5NF?
d.
(
Exercise 1.9
.) Is it true that if a relvar is in BCNF but not 5NF, then it must be all key?
e.
(
Exercise 1.10
.) Can you give a precise definition of 5NF?
f.
(
Exercise 1.11
.) Is it true that 5NF relvars are redundancy free?
10.2
Give as precise a definition as you can of what it means for a relvar to be subject to a join dependency.
10.3
How many JDs hold in the shipments relvar SP?
10.4
What does it mean to say a JD is implied by superkeys?
10.5
What's a trivial JD? Is a trivial FD a special case?
10.6
Give an example of a JD that's (a) tuple forcing, (b) not tuple forcing.
10.7 Consider relvar RAP as discussed in the answer to Exercise 9.2 in Chapter 9. Give examples of an insertion
anomaly and a deletion anomaly that can occur with that relvar.
10.8 The following is a quote from a certain database textbook: “Fifth normal form concerns dependencies that
are rather obscure. It has to do with relations that can be divided into subrelations, as we have been doing, but then
cannot be reconstructed. The condition under which this situation arises has no clear, intuitive meaning. We do not
know what the consequences of such dependencies are or even if they have any practical consequences.” Do you
have any comments?
