GATE | GATE IT 2006 | Question 15

Which of the following relational query languages have the same expressive power?

  1. Relational algebra
  2. Tuple relational calculus restricted to safe expressions
  3. Domain relational calculus restricted to safe expressions

 
(A) II and III only
(B) I and II only
(C) I and III only
(D) I, II and III


Answer: (D)

Explanation:  

Relational algebra is a procedural query language where we input – relations and it yields relations as output. It provides method to get the result. It is performed recursively on a relation and the in between results are relations(output).
Basic set of operations for the relational model. Relational calculus is a non – procedural query language. It provides the query to get result. Higher level declarative language for specifying relational queries. Tupple Relational Calculus operates on each tupple.
Domain Relational Calculus operates on each column or attribute. Safe expression means fixed no. of tupple or column or attribute as a result But all of them has same expressive power. Just different ways to do so.

This solution is  contributed by Mohit Gupta.

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