UGC NET CSE | June 2019 | Part 2 | Question: 31

Question

Which of the following has same expressive power with regard to relational query language?

1. Rational algebra and domain relational calculus
2. Relational algebra and tuples relational calculus
3. Relational algebra and domain relational calculus restricted to safe expression
4. Relational algebra and tuples relational calculus restricted to safe expression

• A. a and b only
• B. c and d only
• C. a and c only
• D. b and d only

Comments

2

Relational Algebra equivalent in expressing power to A. TRC B. DRC restricted to safe Operation.

Answer 1

B) c and d only

A SAFE EXPRESSION is one that is guaranteed to yield a finite number of tuples as its results. Otherwise, it is called UNSAFE.
ex.. {t| ~(t belongs R)} this is unsafe query..