| 51. | Let r be a relation instance with schema R = (A, B, C, D). We define r1 = ΠA, B, C (r) and r2 = ΠA.D (r). Let s = r1 * r2 where * denotes natural join. Given that the decomposition of r into r1 and r2 is lossy, which one of the following is TRUE? |
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Answer: (c).r ⊂ s
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| 52. | Consider a relation scheme R = (A, B, C, D, E, H) on which the following functional dependencies hold: {A–>B, BC–>D, E–>C, D–>A}. What are the candidate keys of R? |
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Answer: (d).AEH, BEH, DEH
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| 53. | The relation scheme Student Performance (name, courseNo, rollNo, grade) has the following functional dependencies: name, courseNo → grade rollNo, courseNo → grade name → rollNo rollNo → name The highest normal form of this relation scheme is |
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Answer: (b).3 NF
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| 54. | Consider the following functional dependencies in a database: Data_of_Birth → Age Age → Eligibility Name → Roll_number Roll_number → Name Course_number → Course_name Course_number → Instructor (Roll_number, Course_number) → Grade The relation (Roll_number, Name, Date_of_birth, Age) is: |
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Answer: (d).None of the above
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| 55. | Relation R with an associated set of functional dependencies, F is decomposed into BCNF. The redundancy (arising out of functional dependencies) in the resulting set relations is. |
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Answer: (a).Zero
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| 56. | With regard to the expressive power of the formal relational query languages, which of the following statements is true? |
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Answer: (c).Relational algebra has the same power as safe relational calculus
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| 57. | Relation R is decomposed using a set of functional dependencies, F and relation S is decomposed using another set of functional dependencies G. One decomposition is definitely BCNF, the other is definitely 3NF, but it is not known which is which. To make a guaranteed identification, which one of the following tests should be used on the decompositions? (Assume that the closures of F and G are available). |
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Answer: (c).BCNF definition
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| 58. | From the following instance of a relation scheme R (A, B, C), we can conclude that : A B C 1 1 1 1 1 0 2 3 2 2 3 2 |
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Answer: (c).B does not functionally determine C
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| 59. | Consider a schema R(A,B,C,D) and functional dependencies A->B and C->D. Then the decomposition of R into R1(AB) and R2(CD) is |
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Answer: (c).dependency preserving but not lossless join
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| 60. | Suppose the adjacency relation of vertices in a graph is represented in a table Adj(X,Y). Which of the following queries cannot be expressed by a relational algebra expression of constant length? |
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Answer: (d).List all vertices reachable from a given vertex
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