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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
  1. II and III only
  2. I and II only
  3. I and III only
  4. I, II and III
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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/

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5 Answers

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Best answer
Answer: D

All are equivalent in expressive power.
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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.
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3 of them have same expressive power
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Relation algebra, tuple calculus and domain calculus are same in power.

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

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