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 reac and write operations on a data element z by a transaction T_{i}, respectively. Consider the schedule S with four transactions.

S : R_{4}(x), R_{2}(x), R_{3}(x), R_{1}(y), W_{1}(y), W_{2}(x), W_{3}(y), R_{4}(y)

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