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GATE IT 2006 | Question: 15

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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

7 Answers

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Option D: Expressive power means whether we can transform a query from one query language to another. Relational Algebra always returns a finite result. Any query written in safe TRC can be converted into an equivalent Relational Algebra query, and any Relational Algebra query can also be converted into an equivalent safe TRC query. Therefore, both have the same expressive power. Similarly, safe DRC can also be converted to and from Relational Algebra, so Relational Algebra, safe TRC, and safe DRC all have the same expressive power.
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