Databases Reference

In-Depth Information

Prove this theorem. Which rules from the previous two exercises did you use? Which rules from those exercises

can be derived as special cases of the theorem?

7.6

Find an irreducible cover for the following set of FDs:

AB
→
C
BE
→
C

C
→
A
CE
→
FA

BC
→
D
CF
→
BD

ACD
→
B
D
→
EF

7.7

Consider the following FDs:

A
→
B

BC
→
DE

AEF
→
G

Is the FD
ACF
→
DG
implied by this set?

7.8

Two sets of FDs are
equivalent
if and only if each is a cover for the other. Are the following sets equivalent?

{
A
→
B
,
AB
→
C
,
D
→
AC
,
D
→
E
}

{
A
→
BC
,
D
→
AE
}

Note that any given set
F
of FDs is certainly equivalent to a set
C
if
C
is an irreducible cover for
F
, and further that

two sets are equivalent if and only if they have the same irreducible cover.

7.9

Relvar
R
has attributes
A
,
B
,
C
,
D
,
E
,
F
,
G
,
H
,
I
, and
J
, and is subject to the following FDs:

ABD
→
E
C
→
J

AB
→
G
CJ
→
I

B
→
F
G
→
H

Is this set reducible? What keys does
R
have?