SQL

(15%) Please refer to a relation S(A,B,C,D,E) with the FD's {ABC,BD,DEA} and answer the following questions. (a) (5%) What are the keys of S ? (A) {A,B,D,E} (B) {A,B} and {D,E} (C) {B,E} (D) {A,B,E} and {B,D,E} (b) (5\%) Suppose we decide to decompose S into S1(B,D) and S2(A,B,C,E). Which of the following statements are true? I. {ABC} is a minimal basis for the FD's that hold in S2. II. ABC is a BCNF violation for S2. III. S2 should be decomposed further into S3(A,B,C) and S4(C,E). (A) I only (B) II only (C) I and II only (D) II and III only (E) I, II, and III (c) (5%) Which of the following statements are true? I. Instead of decomposing S using BD, we could decompose S using DEA first. II. It does not matter whether we start with BD first or DEA first. At the end of the BNCF decomposition algorithm, we will get the same set of relations. (A) I only (B) II only (C) Both I and II (D) Neither I nor