DATABASE SYSTEM CONCEPTS LCPO
DATABASE SYSTEM CONCEPTS LCPO
7th Edition
ISBN: 9781265586577
Author: SILBERSCHATZ
Publisher: MCG
Expert Solution & Answer
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Chapter 7, Problem 30E

a.

Explanation of Solution

To compute B+:

  • To compute B+, the closure of an attribute “B” over a set of functional dependencies “F”, refer the algorithm in Figure 7.19 of the textbook.
  • The result is initialized to {B}.
  • For the first repetition,
    • The condition is not satisfied in first and second functional dependency.
    • The condition B is a subset of {B} is satisfied for the functional dependency BD Hence “D” is added to the result.
      • Therefore, the result = {B,D}.
    • The condition “D” is a subset of {B,D} is satisfied for the functional dependency DA Hence “A” is added to the result

b.

Explanation of Solution

To prove:

“AG” is super key.

Proof:

  • This can be proved by proving the existence of functional dependency so that AGABCDEG It is given that ABCD.
  • The union of the similar sets is the set with itself (AA=A).
  • To get  AABCD, use Armstrong’s augmentation axiom with “A”.
  • BCDE is given and to get ABCDABCDE, use Armstrong’s augmentation axiom with ABCD

c.

Explanation of Solution

Canonical cover:

  • “D” is irrelevant in first and second dependencies because of third dependency.
  • Hence remove the attribute “D” from the first and second functional dependencies to achieve ABC and BCE.
  • According to the sub-part “a”, B+ is computed as {B,D,A,C,E}.
  • The functional dependency BE can be determined from the above set and from this the functional dependency BCE becomes irrelevant

d.

Explanation of Solution

Third Normal Form (3NF) decomposition:

  • In the canonical cover, functional dependency is exists such that the attribute set id is a subset of other dependency.
  • Hence, each functional dependency will generate its own relation.
  • The relations according to the functional dependencies in the canonical cover are,
    • r1(A,B,C)
    • r2(B,D,E)
    • r3(D,A)
  • “G” has to part of all super keys as it is not dependent on any attribute...

e.

Explanation of Solution

Boyce-Codd Normal Form (BCNF) decomposition:

  • To compute the BCNF decomposition of the schema relation “r” using the original set “F” of functional dependency, follow the steps below,
    • For the relation not being in BCNF, the first original functional dependency is responsible.
    • So, according to first functional dependency , the original relation is decomposed as follows,
        ...

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