With regard to the expressive power of the formal relational query languages,…
2002
With regard to the expressive power of the formal relational query languages, which of the following statements is true?
- A.
Relational algebra is more powerful than relational calculus
- B.
Relational algebra has the same power as relational calculus
- C.
Relational algebra has the same power as safe relational calculus
- D.
None of the above
Attempted by 30 students.
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Correct answer: C
The correct answer is Option C. Relational algebra is a procedural formal query language, while relational calculus is declarative. For meaningful finite database queries, relational calculus is restricted to safe expressions, which always produce finite results based on the database contents. Codd’s theorem states that relational algebra and safe relational calculus have the same expressive power. Therefore, relational algebra is not more powerful than safe relational calculus; they are equivalent.