A directory of Objective Type Questions covering all the Computer Science subjects. Here you can access and discuss Multiple choice questions and answers for various compitative exams and interviews.

 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? a. s ⊂ r b. r ∪ s c. r ⊂ s d. r * s = s

 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? a. AE, BE b. AE, BE, DE c. AEH, BEH, BCH d. AEH, BEH, DEH

 53. The relation scheme Student Performance (name, courseNo, rollNo, grade) has the following functional dependencies:name, courseNo → graderollNo, courseNo → gradename → rollNorollNo → name The highest normal form of this relation scheme is a. 2 NF b. 3 NF c. BCNF d. 4NF

 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) → GradeThe relation (Roll_number, Name, Date_of_birth, Age) is: a. In second normal form but not in third normal form b. In third normal form but not in BCNF c. In BCNF d. None of the above

 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. a. Zero b. More than zero but less than that of an equivalent 3NF decomposition c. Proportional to the size of F+ d. Indeterminate

 56. 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

 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). a. Dependency-preservation b. Lossless-join c. BCNF definition d. 3NF definition