DBMS Questions Gate 2005

Question 1 : Which one of the following is a key factor for
             preferring B+trees to binary search trees for indexing
             database relations?

          a) Database relations have a large number of records
          b) Database relations are sorted on the primary key
          c) B+ -trees require less memory than binary search trees
          d) Data transfer from disks is in blocks
Solution : (d) is the correct option. 
           The transfer of data from disk to primary memory is in the
           form of data blocks. If a data block is large, then
           indexing is easy due to this B+ tree.It is better than
           binary search tree if large amount of data can be access.
Question 2 : Which one of the following statements about normal forms
             is FALSE?

          a) BCNF is stricter than 3NF
          b) Lossless, dependency-preserving decomposition into 3NF
             is always possible
          c) Lossless, dependency-preserving decomposition into BCNF
             is always possible
          d) Any relation with two attributes is in BCNF
Solution : (c) is the correct option. Check out the link for
           explanation.
           http://www.edugrabs.com/normal-forms-shortcuts-for-gate-students/
Question 3 : 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
Solution :
          DBMS Questions Gate 2005
Question 4 : 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. R1 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?

          a) 2
          b) 3
          c) 4
          d) 5
Solution :
        QA16- DBMS - Gate 2005 - CS
       (b) is the right answer.
Question 5 : The following table has two attributes A and C where A is the
             primary key and C is the foreign key referencing A with
             on delete cascade.
A C
2 4
3 4
4 3
5 2
7 2
9 5
6 4
             The set of all tuples that must be additionally deleted to
             preserve referential integrity when the tuple (2,4) is
             deleted is:

          a) (3,4) and (6,4)
          b) (5,2) and (7,2)
          c) (5,2), (7,2) and (9,5)
          d) (3,4), (4,3) and (6,4)
Solution :
          QA17- DBMS - Gate 2005 - CS
          So, (c) is the right answer.
Question 6 : The relation book (title, price) contains the titles and
             prices of different books. Assuming that no two books
             have the same price, what does the following SQL query
             list?

             select title
             from book as B
             where (select count(*)
             from book as T
             where T.price > B.price) < 5

          a) Titles of the four most expensive books
          b) Title of the fifth most inexpensive book
          c) Title of the fifth most expensive bookTitles of the
             five most expensive books
          d) Titles of the five most expensive books
Solution :
         QA18- DBMS - Gate 2005 - CS
Question 7 : 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
Solution :
         QA19- DBMS - Gate 2005 - CS
     

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