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Thread: Normalisation

  1. #1
    Join Date
    Jan 2003
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    1

    Normalisation

    How do you represent an arc relationship in an ERD when you normalise the data?

    Thanks

  2. #2
    Join Date
    Sep 2002
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    UK
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    Re: Normalisation

    Originally posted by Joanna
    How do you represent an arc relationship in an ERD when you normalise the data?

    Thanks
    I'm not sure I understand your question. In the barker notation for ERDs an arc is shown by joining the relationships with a symbol rather like a bracket. The nearest I can manage here is:

    Person --------(--< Address
    Organisation ---(--<

    (An address is related to a Person OR an Organisation).

  3. #3
    Join Date
    Jan 2003
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    14
    Hum, it's me again!
    So in the birdwatching / trainspotting scenario where you told me there could be an exclusive relationship (the birdwatcher could report the bird or the class of bird if he/she didn't know the right name but not both as it would be redundant since the bird is part of the birdclass how would this exclusive relationship appear when the data are normalised?

    By the way, I'm not encroaching on Joanna's territory, we are working on the same project!!!
    ariane

  4. #4
    Join Date
    Sep 2002
    Location
    UK
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    Oh no, not you again!!!

    Well, I struggle to show this without doing a real diagram but:

    BirdClass ----< Bird ---(< Sighting
    |----------------------(<

    i.e. Sighting may be for a Bird OR a BirdClass (not both). When Sighting is for a Bird then the BirdClass is derived from the Bird-BirdClass relationship.

    I'll attempt to attach a proper diagram...
    Attached Thumbnails Attached Thumbnails erd.bmp  

  5. #5
    Join Date
    Jan 2003
    Posts
    14
    Thanks for the picture!!!
    Ok I'm nearly there but would the normalisation I've attached be ok?

    Thank you! (You must be totally sick of me by now!!!)
    Attached Files Attached Files
    ariane

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