COMP2400/COMP6240 - Relational Databases代写

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    • COMP2400/COMP6240 - Relational Databases代写
    COMP2400/COMP6240 - Relational Databases
    Assignment 2
    Due date: 10am, 27 September 2016
    This assignment will be marked out of 10. It will count for 10% of the nal grade. Below
    you will nd 4 questions to reach this score. Marks are assigned for the process of nding
    a solution, not only for the result. Hence, include all essential ideas and steps that are
    necessary to derive a solution.
    Instructions:
     This assignment should be done individually or by a pair of students.
     Your submission must include Assignment Cover Sheet, which is available from the
    course website on Wattle.
     Hand written submissions will not be marked.
     You need to submit your assignment as a hard copy to the assignment box in the
    student foyer (i.e., on the ground 
    oor of the CSIT building). You are also
    required to submit an electronic copy on Wattle.
     Late submission, unless authorized by the lecturers, will attract the penalties 5% per
    day. If submitted after one week of its deadline, the assignment will not be marked.
     Plagiarism will attract academic penalties in accordance with the ANU guidelines.
    Good luck and enjoy the time you will spend on this assignment.
    Question 1 1 Mark
    Suppose R is a relation with four attributes ABCD and the only keys are AB and BD. How
    many superkeys R has? Explain why.
    1
    2 Assignment 2
    Question 2 2 Marks
    Consider a relation schema R with ve attributes ABCDE and the following functional
    dependencies on R:
     = fA ! C;C ! E;EB ! A;A ! E;AD ! Bg
    2.1 Find all the keys of R with respect to . Justify your answer (i.e., include the steps
    used for nding the keys).
    (1 Mark)
    2.2 Does  j= CD ! B hold? If it holds, explain why it holds. If it does not hold, give a
    relation that contains only two tuples, as a counterexample, to show it does not hold.
    (0.5 Mark)
    2.3 Does  contain any redundant functional dependencies? A functional dependency
    X ! Y is redundant if we remove it from , and we can still infer X ! Y from the
    functional dependencies in