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Avatto > > UGC NET COMPUTER SCIENCE > > PRACTICE QUESTIONS > > Database > > Data Modeling

61. Let R is a relation schema, R(A, B, C, D) and F = {A —> B, B --> C, C —> A) is the set of functional dependency. Determine the key of relation ?

  • Option : D
  • Explanation : Rule to find out the key in relation :- Key ---> Rest of Attributes As Key determies rest of the attributes Key must include all attributes but can not be on RHS of any functional dependency i.e Only fields on RHS are determined. An undetermined field must be in the key. REST must include all attributes but NOT on LHS They don't determine anything so they can not be part of key. If field is not in ANY FD, it must be part of the key Now considering these 5 points we get D as Key.
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62. Which of the following statement is correct?

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63. Given the basic ER and relational model which of the following is incorrect?

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64. Let r be a relation instance with schema R = (A, B, C, D). We define r1 =∏ A,B,C (r) and r2 = ∏A, 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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65. Let E1 and E2 be two entities in an E/R diagram with simple single-valued attributes. R1 and R2 are two relationships between E1 and E2, where R1 is one-to-many and R2 is many-to-many. RI and R2 do not have any attributes of their own. What is the minimum number of tables required to represent this situation in the relational model?

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