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  1. #1
    Join Date
    Apr 2015
    Posts
    2

    Question Inheritance relationship in ERD diagrams

    Hi Everyone,

    This my first post here, and I hope I will get the right answer I have already asked it on StackOverflow, but nobody has answered it.
    I have question about inheritance representation in ERD-diagram. The following example: I have plane, and I have also two types of planes
    1-PersonsPlane
    2-CargoPlane
    I am confused which relationship to use ( 1-to-1 OR 1-to-Many). My DB teacher told me that I should use 1-to-1 relationship, But I have found on internet many examples use (1-to-Many) relationship instead of (1-to-1) . Check these images:

    (1-to-1)
    Click image for larger version. 

Name:	aafSi.png 
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ID:	16316

    (1-to-Many)
    Click image for larger version. 

Name:	1TOMANY.png 
Views:	4 
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ID:	16317

    Personally I think that it should be (1-to-Many) because at a specific moment, in general, a Super Entity can have more than one child. So in our example here: a plane can be 3 persons-planes and 4 cargo-planes.

  2. #2
    Join Date
    Feb 2004
    Location
    New Zealand
    Posts
    1,418
    (1-to-many)

    as one plane can have many Person

    and one plane can have many cargo in it

    You need to think about

    can a personplane be a cargoplane

    and can a caroplane be a personplane

    if not the I would just call it a plane and have a Dropdown selection what plane is it




    also just to get you thinking hat

    (1 to many)-(many to 1)
    hope this help

    See clear as mud


    StePhan McKillen
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  3. #3
    Join Date
    Apr 2015
    Posts
    2
    Quote Originally Posted by myle View Post
    (1-to-many)

    as one plane can have many Person

    and one plane can have many cargo in it

    You need to think about

    can a personplane be a cargoplane

    and can a caroplane be a personplane

    if not the I would just call it a plane and have a Dropdown selection what plane is it




    also just to get you thinking hat

    (1 to many)-(many to 1)
    Sorry, but I didn't understand you! What do you mean exactly?

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