Databases Test ...

Consider a relation R(ABCDE) and the primary key is A E. In the given relational schema which of the following is not a superkey?

Consider the relation R(X, Y, Z, W, V) in which X, Y, Z, W, and V are the attributes and the following set of functional dependencies

A = { {X, Y} → {Z, W},  {X, W, V} → {Q, R}  }

Which of the following is the trivial functional dependency in A+, where A+ is closure of A?

Let R₁(a, b, c) and R₂(x, y, z) be two relations in which a is the foreign key of R₁ that refers to the primary key of R₂. Consider following four options.

(a) Insert into R₁

(b) Insert into R₂

(c) Delete from R₁

(d) Delete from R₂

Which of the following is correct about the referential integrity constraint with respect to above?

Consider the relational schema R(A B C D) with following functional dependency set F = {A → BC, C → D}; The relation R is in _____

Suppose T₁(P, Q) and T₂(R, S) are two relation schemas. Let t₁ and t₂ be the corresponding relation instances. R is a foreign key that refers to P inT₁. If data in t₁ and t₂ satisfy referential integrity constraints, which of the following is/are always true?

I. ∏_R (t₂) – ∏_P(t₁) = Φ

II. ∏_P(t₁) ≠ ∏_R(t₂)

Consider the relational schema R = (P, Q, R, S, T, U) on which the following functional dependencies hold:

F = {P ➝ Q, QR ➝ S, T ➝ R, S ➝ P}

How many candidate keys are present in R?

Which of the following statements are not correct?

S1: 3NF decomposition is always Lossless join and dependency preserving.

S2: 3NF decomposition is always lossless join but may or may not be dependency preserving.

S3: BCNF decomposition always lossless join and dependency preserving.

Consider the schem a a r(A, B, C, D, E) with the following functional dependencies:

A → BC

CD → E

B → D

E → A

The decomposition of the schema into r₁(A, B, C) and r₂(A, D, E) is _________.

Which of the following is/are false for the relational table R?

I. In BCNF, R has a nontrivial functional dependency Y → X, where Y is not a superkey and X is a prime attribute.

II. In 3NF, R has a nontrivial functional dependency Y → X, where Y is not a superkey and X is a non-prime attribute and Y is a proper subset of some key.

III. In 2NF, R has a nontrivial functional dependency Y → X, where Y is a superkey.