Relational Calculus ↩

• Codd’s Theorem

    > Any query in a language is expressible using relational calculus.
    > The language is relationally complete.
  

• Two variants:
  • Tuple relational calculus

  • Domain relational calculus

Tuple Relational Calculus

• T is a variable - tuples of a relation as values : {(T

  P(T)}

• {(T	T ∈ instructor ∧ T.salaray ≥ 90000)} –> Selection

• {(T	∃R ∈ instructor(T.name = R.name ∧ R.salary ≥ 90000)} –> Projection

Domain Relational Calculus

• Domain variable - range of domain values : {(A1,A2,…,An)

  P(A1,A2,…,An)}

• {(I,N,D,S)

  (I,N,D,S) ∈ instructor ∧ S ≥ 90000)}