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Thread: E/R notation

  1. #1
    Join Date
    Apr 2004
    Location
    Sweden
    Posts
    17

    Question E/R notation

    Hi there!

    I'm quite a newbie to E/R notaions and therefore I have the following questions:

    1. In Microsoft Visio one can choose from two symbol-sets: IDEF1X and Relational....

    I don't quite understand when to use the Relational-set because I can't see that it gives any information about the cardinality (min, max) constraints with the notation of arrows. I have seen a tutorial where one first use the Relational symbolset (arrows) and then fine-tune with crow feet (IDEF1X-notation)...is this what the Relational-symbolset is for - to make rough sketches?

    2. How is the constraints symbolised with chicken/crowfeets and so on implemented in the database? f.i in a MySql-database?

    3. what is the difference between crow-feet and chicken-feet?

    Sorry for posting this in two different forums....I posted the first copy by mistace...

    Thanks in advance!

    /Marcus

  2. #2
    Join Date
    Feb 2004
    Location
    In front of the computer
    Posts
    15,579
    ERD notations are much like religions... There are a gazillion variations, and each one is espoused as the "one true faith" by its adherants. Anyone that believes otherwise must be a heretic!

    My advice is to pick a notation that suits your needs, and stay with it. Be aware of the other notations, because they all have some unique features and value.

    I'm a crusty old phart, that learned IDE1FX a very long time ago, and have never seen any real reason to change. When I deal with folks that prefer another notation, I switch that project to their notation of preference, but I usually continue to work IDE1FX just because it is what I'm most comfortable using, which allows me to see and avoid problems more easily!

    -PatP

  3. #3
    Join Date
    Feb 2004
    Posts
    108
    Originally posted by Pat Phelan
    ERD notations are much like religions...
    -PatP
    Very true.

    Besides this you can always keep a legend in your diagram - indicating each symbol and it's meaning.

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