ITPEC FE Morning October 2018 Question 27

Relational Table Decomposition — split attributes into tables preserving foreign key relationships.

Given functional dependencies:
- a → b, c, d, e
- b → f, g, h
- e → i, j

Correct decomposition into 3 tables:

• •Table 1 (a, b, c, d, e) — PK: a, with b and e as foreign keys
• •Table 2 (b, f, g, h) — PK: b, referenced by Table 1
• •Table 3 (e, i, j) — PK: e, referenced by Table 1

Why not others:
- (a) — Table 1 has only a; no FK columns to link to Table 2 or Table 3
- (c) — mixes b's dependents (f, g, h) into Table 1; violates FD grouping
- (d) — Table 1 is (a, c, d) with no b or e, so no FK links to other tables

Key rule: When decomposing, keep FK columns in the referencing table so relationships between tables are preserved.

AI-generated — may contain errors