Define the basic operations of the relational algebra?   

 Ans: Basic operators of relational algebra are:

1. Union (∪) - Selects tuples which are in either P or Q or in both of them.  The duplicate tuples are removed.

R = P ∪ Q

 2. Difference or Minus (-) - eliminates common tuples from the first relation.

R = P - Q 

3.  Cartesian Product or Cross Product (×) - The cartesian product of two relations is the concatenation of tuples that are belonging to the two relations and containing all possible combination of the tuples.

R = P× Q

 4. Projection (π) - The projection of a relation is illustrated as a projection of all its tuples over some set of attributes that is it yields a vertical subset of the relation. The relation's projection T on the attribute A is presented by T [A] or π_A(T),.

 5. Selection (σ) - Selects just some of the tuples, those satisfy specified criteria, from the relation. It yields a horizontal subset of a following relation.

R = σ_B(P)