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  1. #1
    Join Date
    Apr 2011
    Posts
    4

    Unanswered: Howto check for Database BCNF violations?

    How do they determine the FD's?
    Are superkeys any attributes that are not keys?
    Why does name → addr violate BCNF?
    Why does beersLiked→ manf violates BCNF?

    Here is the example of the relation:

    Code:
    R = Drinkers(name, addr, beersLiked, manf, favoriteBeer)
    F Ds:
     name → addr
     name → favoriteBeer
     beersLiked→ manf
    Pick BCNF violation name → addr.
     Close the left side: name + = name addr favoriteBeer.
     Decomposed relations:
    Drinkers1(name, addr, favoriteBeer)
    Drinkers2(name, beersLiked, manf)
     Projected FDs (skipping a lot of work):
     For Drinkers1: name → addr and name → favoriteBeer.
     For Drinkers2: beersLiked→ manf.
    
    BCNF violations?
     For Drinkers1, name is key and all left sides
    of FDs are superkeys.
     For Drinkers2, {name, beersLiked} is the key,
    and beersLiked→ manf violates BCNF.
    
    Decompose Drinkers2
     Close beersLiked + = beersLiked, manf.
     Decompose:
    Drinkers3(beersLiked, manf)
    Drinkers4(name, beersLiked)
     Resulting relations are all in BCNF:
    Drinkers1(name, addr, favoriteBeer)
    Drinkers3(beersLiked, manf)
    Drinkers4(name, beersLiked)

  2. #2
    Join Date
    Sep 2001
    Location
    Chicago, Illinois, USA
    Posts
    601
    Come on!

    People do not talk in acronyms and people should not write in acronyms without explaining what they are writing. [unless they are trying to impress other people--which does not impress me]

    On first reference to an acronym, spell it out so that everyone can understand exactly what you are saying.

    So, you would express FD as functional dependencies (FD) and Boyce-Codd Normal Form (BCNF).
    Ken

    Maverick Software Design

    (847) 864-3600 x2

  3. #3
    Join Date
    Jan 2003
    Location
    Massachusetts
    Posts
    5,800
    Provided Answers: 11
    Maybe you should post your class notes about the definitions of some of those acronyms.

  4. #4
    Join Date
    Apr 2011
    Posts
    4
    Quote Originally Posted by PracticalProgram View Post
    Come on!

    So, you would express FD as functional dependencies (FD) and Boyce-Codd Normal Form (BCNF).

    That would be correct. Sorry...thought it would be a well known part of DBMS.

  5. #5
    Join Date
    Mar 2003
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    6,102
    Provided Answers: 1
    You're going to get steam rolled by the members for flat out asking us to do your homework.

    Heads up.
    oh yeah... documentation... I have heard of that.

    *** What Do You Want In The MS Access Forum? ***

  6. #6
    Join Date
    Apr 2011
    Posts
    4
    Quote Originally Posted by Teddy View Post
    You're going to get steam rolled by the members for flat out asking us to do your homework.

    Heads up.
    This isn't homework. If you google any of the example into what I have posted you will see it's straight from a Stanford Powerpoint. I just want to understand it better...that's all.

  7. #7
    Join Date
    Feb 2004
    Location
    One Flump in One Place
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    14,912
    Those dependencies don't violate BCNF as such. They violate a lower normal form.
    Can you post a link to your source?
    Testimonial:
    pootle flump
    ur codings are working excelent.

  8. #8
    Join Date
    Apr 2011
    Posts
    4
    Quote Originally Posted by pootle flump View Post
    Those dependencies don't violate BCNF as such. They violate a lower normal form.
    Can you post a link to your source?

    http://www.google.com/url?sa=t&sourc...l5ARzw&cad=rja

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