views in relational algebra 1 basic

Question

Views in relational algebra: 

 1. Basic expression contains either 

a) A relation in the database.

b) A constant relation.

2.  General expressions are madde out of smaller sub expressions using 

a) σ_p(E₁) select (p a predicate) 

b) ∏s(E₁) project (s a list of attributes) 

c) P_x(E₁)rename (x a relation name) 

d) E₁∪E₂ union

e) E₁- E₂ set difference 

f) E_1x x E₂ cartesian product