# Database management system - Theory of computation

CSE - Database management system - Theory of computation
Question:-
Option (A)
R is many-many from E to F
Option (B)
R is one-one from E to F
Option (C)
R is many-one form F to E
Option (D)
None of these
Correct Option:
B
Question Solution:
Exp. Referential integrity is an constraint added to many-one relationship in the "one direction". Since a one-one relationship is a special case of a many-one relationship so R may be one-one from E to F.
Question:-
Option (A) Option (B)
Option (C)
-
Option (D)
σ
Correct Option:
C
Question Solution:
Exp.Only the difference operator is not monotone. In the expression A-B, adding more tuples to B can actually make the answer smaller.
Question:-
Option (A)
S1 only
Option (B)
S1 and S2 only
Option (C)
S1, S2 and S3
Option (D)
None of these
Correct Option:
A
Question Solution:
Exp.S1 : A, B and DE are keys of R. So statement S1 is true.
S2 : R is not in 3NF. Because D->C is non trivial; but D is not a superkey while C is not part of some key. So statement S2 is false.
S3 : R is not in BCNF. D->C is non trivial, but D is not a superkey. So statement S3 is false.
So only statement S1 is true.
Question:-
Option (A)
4
Option (B)
6
Option (C)
8
Option (D)
5
Correct Option:
B
Question Solution:
Exp.The keys could be {{A}, {B}, {C}} or {{A, B}, {B, C}, {A, C}}. Thus there are 3 keys at the same time. For four attributes, the answer is not 4. It is 6 :{{A}, {B}, {A, C}, {A, D}, {B, C}, {B, D}, {C, D}}.