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  1. #1
    Join Date
    Oct 2008
    Posts
    5

    non redundant covers

    Hi,

    Does anybody have some theoretical idea about functional dependencies.

    I have to find non redundant covers and convert a relation to BCNF. But i am unable to understand the concept.

    My question is:

    Consider the following relations and the set of Function Dependencies(FDs):
    SHIPMENT (ship_id, S_capacity, S_date, cargo, amount)
    FDs are as follows:
    Ship_id -->S_capacity
    Ship_id, S_date --> cargo
    Cargo, S_capacity --> amount

    Now perform the following:
    (i) Identify the key of the relation.
    (ii) Find the non-redundant cover of the given FDs.
    (iii) Normalize the relation into BCNF. Is the decomposition dependency preserving? Give reason for your answer.

    Anyone who can help me out??????

  2. #2
    Join Date
    Apr 2002
    Location
    Toronto, Canada
    Posts
    20,002
    homework!!!

    no, nobody here can help you

    rudy.ca | @rudydotca
    Buy my SitePoint book: Simply SQL

  3. #3
    Join Date
    Jan 2007
    Location
    UK
    Posts
    11,434
    What Rudy means is - we aint doing it for you!
    Do the assignment as best as you can and you can ask for critique here.
    George
    Home | Blog

  4. #4
    Join Date
    Jun 2003
    Location
    Ohio
    Posts
    12,592
    Quote Originally Posted by mayurgogia
    Does anybody have some theoretical idea about functional dependencies.
    Sure. This guy has nothing but theoretical ideas about functional dependencies: http://www.dbforums.com/showthread.php?t=1633864
    If it's not practically useful, then it's practically useless.

    blindman
    www.chess.com: "sqlblindman"
    www.LobsterShot.blogspot.com

  5. #5
    Join Date
    Oct 2008
    Posts
    5
    Yes... Thanks all....
    Finally I found it myself...... though it was difficult to understand from books...
    (i) Key for the relation is (ship_id,s_date) because there does not exist any dependency as R-->key for key being a proper subset of R+. and all attributes are dependent on the key.
    (ii) None of the given dependencies is redundant. So, non redundant cover for the dependency set is (Ship_id -->S_capacity;Ship_id, S_date --> cargo;Cargo, S_capacity --> amount)
    (iii)Converting to the BCNF gives the following three relations for breakup of the given one:
    shipment1(Ship_id,S_capacity);
    shipment2(ship_id,s_date);
    shipment2(ship_id,Cargo,amount)

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