A relation r(A, B) in a relational database has 1200 tuples. The attribute A has integer values ranging from 6 to 20, and the attribute B has integer values ranging from 1 to 20. Assume that the attributes A and B are independently distributed. The estimated number of tuples in the output of σ_{(A>10)∨(B=18)}(r) is ______

The following relation records the age of 500 employees of a company, where empNo (Indicating the employee number) is the key:

empAge(empNo, age)

Consider the following relational algebra expression:

π_empNo(empAge ⋈ _(age>age1) ρ_{empNo 1, age1}(empAge))

What does the above expression generate?

Consider the relation R(P, Q, S, T, X, Y, Z, W) with the following functional dependencies.

PQ → X; P → YX; Q → Y; Y → ZW

Consider the decomposition of the relation R into the constituent relations according to the following two decomposition schemes.

D₁ : R = [(P, Q, S, T); (P, T, X); (Q, Y); (Y, Z, W)]

D₂ : R = [(P, Q, S); (T, X); (Q, Y); (Y, Z, W)]

Which one of the following options is correct?

Let r_i(z) and w_i(z) denote read and write operations respectively on a data item z by a transaction T_i. Consider the following two schedules.

S₁ : r₁(x) r₁(y) r₂(x) r₂(y) w₂(y) w₁(x)

S₂ : r1(x) r₂(x) r2(y) w2(y) r₁(y) w1(x)

Which one of the following options is correct?