Question: Let R A B and S A C and let r R and s S be relation

Let R = (A, B) and S = (A, C), and let r(R) and s(S) be relations. Write relational-algebra expressions equivalent to the following domain-relationalcalculus expressions:
a. {< a > | ∃ b (< a, b >∈ r ∧ b = 17)}
b. {< a, b, c > | < a, b >∈ r ∧ < a, c >∈ s}
c. {< a > | ∃ b (< a, b >∈ r) ∨ ∀c (∃ d (< d, c >∈ s) ⇒ < a, c >∈ s)}
d. {< a > | ∃ c (< a, c > ∈ s ∧ ∃ b1, b2 (< a, b1 > ∈ r ∧ < c, b2 > ∈ r ∧ b1 > b2))}

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  • CreatedJanuary 28, 2011
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