GATE | GATE-CS-2002 | Question 20

With regard to the expressive power of the formal relational query languages, which of the following statements is true?
(A) Relational algebra is more powerful than relational calculus
(B) Relational algebra has the same power as relational calculus
(C) Relational algebra has the same power as safe relational calculus
(D) None of the above


Answer: (C)

Explanation:
A query can be formulated in relational calculus if and only if it can be formulated in relational algebra. So, relational algebra has the same power as relational calculus.

But, it is possible to write syntactically correct relational calculus queries that have infinite number of answers. Such queries are unsafe.
Queries that have an finite number of answers are safe relational calculus queries.

Thus, Relational algebra has the same power as safe relational calculus.

 
Thus, option (C) is the answer.

 
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