Results 1 to 3 of 3
  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 
Views:	5 
Size:	30.2 KB 
ID:	16316

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

Name:	1TOMANY.png 
Views:	4 
Size:	31.3 KB 
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
    1,468
    (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

    StePhan McKillen
    the aim is store once, not store multiple times
    Remember... Optimize 'til you die!
    Progaming environment:
    Access based on my own environment: DAO3.6/A97/A2000/A2003/A2007/A2010
    VB-NET based on my own environment started 2007
    SQL-2005 based on my own environment started 2008
    YOUR PASSWORD IS JUST LIKE YOUR TOOTHBRUSH DON'T SHARE IT.
    DONT WORRY ABOUT THOSE WHO TALK BEHIND YOUR BACK
    THEY'RE BEHIND YOU FOR A REASON

  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?

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •