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  1. #1
    Join Date
    Nov 2009
    Posts
    1

    Weak entity decision making (ER diagrams)

    First of all thank you in advance for any help that you can offer me.

    I am currently drawing up an ER diagram of World countries, and I am finding it hard to decide whether to use a weak entity or not. If I have a country entity for example, and had to describe which country bordered which other country, would this be a weak entity due to the fact that the border information is meaningless without knowledge of the country itself? My logic was that if a country was deleted from the database, then you would want to cascade the deleting down to the border attributes automatically too. I would just like a quick opinion if at all possible please.

    Thank you for your help.

  2. #2
    Join Date
    Dec 2007
    Location
    London, UK
    Posts
    741
    I wouldn't spend too much time actually deciding whether to use a weak entity. Design your model based on formal methods like ORM or guiding principles like Normalization and so on. If some of the entities thus identified are "weak" then so be it. The weak entity concept is of very little importance in relational database design.

    I think you are right. I expect you wouldn't want a border referring to a country that no longer existed in the database.

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