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  1. #1
    Join Date
    Nov 2011
    Posts
    2

    Weak associative entity with primary key

    (I've been looking for this everywhere, to no avail. I thought this would be a much more common question than it is. Hopefully this will be helpful for other people who arrive here googling for this.)

    I have an associative entity whose primary key are three attributes: one belonging to itself, and the foreign keys from the two strong entities it connects (and so a weak associative entity). I have an E-R model to draw, and from what I recall once I indicate an attribute of the associtative entity as key, the scheme is read as having that attribute as the the primary key only. How do I signal in an E-R model that the key is not only that attribute, but the triplet consisting of that attribute and the foreign keys? Can that be done by underlining said attribute with a dashed line instad of a solid line like this:

    http://www.dbforums.com/attachment.p...1&d=1320434563

    Or by doing that and also representing the associative entity with a double rectangle like a regular weak entity has, like this?

    http://www.dbforums.com/attachment.p...1&d=1320434563
    Attached Thumbnails Attached Thumbnails img1.png   img2.png  

  2. #2
    Join Date
    Nov 2011
    Posts
    2
    DEAR PEOPLE FROM THE FUTURE: here's what we've figured out so far...

    ... I asked my teacher, and he doesn't know of any standard to do what I wanted to do. He told me that most likely I would be better off restructuring into weak entities (not associative). I had a weak associative entity in two places, and while he was right about one of them, the other is just better the way it is. I decided to just use my first suggestion:
    http://www.dbforums.com/attachments/...y-key-img1.png

    Since it's clear enough what it means.

    People from the future, you're welcome.

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