QUESTION 47

A referential integrity constraint states

a. a foreign key attribute value must refer to an existing primary key value.

b. a foreign key attribute value can be null.

c. either a. or b.

d. neither a. nor b.

QUESTION 48

Which of the following statement(s) is(are) correct?

a. Multi-level index is designed to reduce the search cost of index part with a reduction ratio of logarithm function.

b. Multi-level index is guaranteed to have the search cost proportional to the number of levels inmulti-level index.

c. Both a. and b. are correct.

d. Neither a. nor b. is correct.

QUESTION 49

The purpose of three level database architecture is to support

a. data dependence

b. data independence

c. both a. and b.

d. neither a. nor b.