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  1. #1
    Join Date
    Dec 2007
    Posts
    6

    find all the candidate keys.

    Would someone please confirm that I have done this correctly. I would really appriciate it.

    Find all of the candidate keys

    R(ABCDEF)
    F={AB > C, C > A, BC > D, ACD > B, D > EF, BE > C, CF > BD, CE > A}

    A = {A}
    B = {B}
    C= {C,A}
    D= {D,E,F}
    E = {E}
    F= {F}
    ______________

    AB = {A,B,C,D,E,F}
    AC={A,C}
    AD={A,D,E,F}
    AE={A,E}
    AF={A,F}
    BC={B,C,A,D,E,F}
    BD={B,C,A,D,E,F}
    BE={B,C,A,D,E,F}
    BF={B,F}
    CD={C,A,D,E,F}
    CE={C,A,E}
    CF={C,A,E,B,D}
    DE={D,E,F}
    DF={D,E,F}
    EF={E,F}
    ________________

    ABC={A,B,C,D,E,F}
    ACD={A,B,C,D,E,F}
    ADE={A,D,E,F}
    AEF={A,E,F}
    BCD={A,B,C,D,E,F}
    BDE={A,B,C,D,E,F}
    BEF={A,B,C,D,E,F}
    CDE={A,B,C,D,E,F}
    CEF={A,B,C,D,E,F}
    DEF={D,E,F}
    ________________

    KEYS:
    AB
    BC
    BD
    BE
    ACD
    ABC
    BCD
    BDE
    BEF
    CDE
    CEF

  2. #2
    Join Date
    Jun 2007
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    London
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    this wouldn't be homework by any chance would it?

  3. #3
    Join Date
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    out on a limb
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    phrased like that... no way is it homework, c'mon Mike get a grip







    ...as if
    I'd rather be riding on the Tiger 800 or the Norton

  4. #4
    Join Date
    Dec 2007
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    6
    wh am I not allowed to get help here. Usually in most forums, when a poster makes a valid attempt, the user community is more than happy to help.

  5. #5
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    Jun 2007
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    No-one is stopping you from getting a better mark in your homework. It's just we'd rather you put in the effort yourself rather than asking professionals to finish it off for you. Of course if you have a particular question on database theory then we'll be happy to help. Would your lecturer be keen on the idea of his students getting help in this way to do their homework? and if not, do you think it might be because he'd view this as cheating?

  6. #6
    Join Date
    Dec 2007
    Posts
    6
    This is clearly not cheating as the homework is not being graded. And I did finish it mylself. I am only asking for some confirmation that I did it correctly. I would rather find out if I am wrong now, and correct my mistakes than to find out during class next Thursday.

  7. #7
    Join Date
    Apr 2002
    Location
    Toronto, Canada
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    20,002
    i like your honesty, and your desire to learn

    would it be okay if we told you next friday?
    rudy.ca | @rudydotca
    Buy my SitePoint book: Simply SQL

  8. #8
    Join Date
    Dec 2007
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    6
    Look, if I can't get help here, I will just go somewhere else. Obviously this place does not operate like other forums. All I wanted was some guidance. It is a shame that the users here are very imature.

  9. #9
    Join Date
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    Quote Originally Posted by gammaman View Post
    Obviously this place does not operate like other forums.
    yup, and we see our reluctance to just hand out homework answers as a good thing

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

  10. #10
    Join Date
    Jun 2004
    Location
    Arizona, USA
    Posts
    1,848
    Quote Originally Posted by r937
    ...we see our reluctance to just hand out homework answers as a good thing
    It's good for you, as you learn the subject, not learn how to copy/paste.

    It's good for us, as we don't get stuck working with/covering for someone who only knows how to copy/paste

    It's good for our employers, as THEY don't have to spend money firing an incompetent, and hiring someone else. Nor do they have to pay us to fix things that could have been done correctly the first time around...
    Lou
    使大吃一惊
    "Lisa, in this house, we obey the laws of thermodynamics!" - Homer Simpson
    "I have my standards. They may be low, but I have them!" - Bette Middler
    "It's a book about a Spanish guy named Manual. You should read it." - Dilbert


  11. #11
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    Quote Originally Posted by gammaman View Post
    Look, if I can't get help here, I will just go somewhere else. Obviously this place does not operate like other forums. All I wanted was some guidance. It is a shame that the users here are very imature.
    You've got a good point, if you can't get an answer here you can certainly look elsewhere. That's a "mixed bag" in that you'll get many answers of varying quality and from different degrees of background and insight, but you probably don't have the experience to efficiently separate the wheat from the chaff yet.

    You've gotten rougher treatment than I think you deserve. You've presented a good bit of work and asked for confirmation.

    The problem is that we (the members of DBForums) have been abused so much, for so long, by so many that we've become very skeptical of students looking for help with homework. Many of us have hired folks that managed to pass classes by turning in what was effectively plagerized homework. This is very, very disappointing to us because we spend weeks or months trying to get the new person to "live up to their potential" only to discover that they have no potential... All of their work has been effectively "stolen" from others, leaving us holding the bag (and I won't go into what the bag is full of at that point).

    Your best bet is to either discuss this with your lecturer or one of their assistants. If that isn't possible, compose a few specific questions about the work you've done so far. I'm pretty sure that you'll get more open and helpful responses to specific questions than a simple "Is this Ok to turn in?" kind of question. The conversation that ensues will almost certainly get you to the point where you're confident in your answer or it will help you develop better/more specific questions.

    I understand that you feel you've gotten a raw deal, and that feeling is justified. On the other hand, we've gotten an equally raw deal, spread over years, that has cost us actual time/work/money. Work with us a bit, I'll make an effort to work with you.

    -PatP
    In theory, theory and practice are identical. In practice, theory and practice are unrelated.

  12. #12
    Join Date
    Dec 2007
    Posts
    6
    OK then just answer this. In my original post for the double attribute AB, can I say that AB > C and then since the set now has {ABC} can I then say that BC goes to D and then D > EF to get a complete set, OR must I say that since BC > D and D > EF that BC >EF, if so than how do I get D for attibute AB?

  13. #13
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    Quote Originally Posted by gammaman View Post
    OK then just answer this. In my original post for the double attribute AB, can I say that AB > C and then since the set now has {ABC} can I then say that BC goes to D and then D > EF to get a complete set...
    Sorry, I've been up to my eyebrows in work. The first of the two plans you discussed is correct.

    -PatP
    In theory, theory and practice are identical. In practice, theory and practice are unrelated.

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