GATE IT 2006 | Question: 15

Question

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

Comments

what is the meaning of "restricted to safe expressions" ?

@Bikram sir

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@ set2018 

A safe expression means an expression which must always produce a finite number of tuples as its result .

see these for example :  http://people.cs.pitt.edu/~chang/156/10calculus.html

http://www.w3schools.in/dbms/relational-calculus/

Answer 1

Answer: D

All are equivalent in expressive power.

Comments

What if "restricted to safe expressions" is not given in question ??

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Then all have different expressive power

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Any proof, please share.

Answer 2

3 of them have same expressive power

Answer 3

Relation algebra, tuple calculus and domain calculus are same in power.

Comments

Relation algebra, safe tuple relational calculus and safe domain relational calculus are same in power.. so option D is correct.

Answer 4

Relational algebra has same expressive power as relational calculus (tuple relational calculus and domain relational calculus)  and these all are relational query languages.

so option D is true