In a relational data model, which one of the following statements is TRUE?

Consider the following three relations in a relational database.

Employee ( $$\underline {eld} $$ , Name), Brand ( $$\underline {bld} $$ , bName), Own ( $$\underline {eld} $$ , $$\underline {bld} $$)

Which of the following relational algebra expressions return the set of elds who own all the brands?

Consider a relation R(A, B, C, D, E) with the following three functional dependencies.

AB $$\to$$ C ; BC $$\to$$ D ; C $$\to$$ E;

The number of superkeys in the relation R is _________.

Let R_i(z) and W_i(z) denote read and write operations on a data element z by a transaction T_i, respectively. Consider the schedule S with four transactions.

S : R₄(x), R₂(x), R₃(x), R₁(y), W₁(y), W₂(x), W₃(y), R₄(y)

Which one of the following serial schedules is conflict equivalent to S?