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  1. #1
    Join Date
    Nov 2007
    Posts
    9

    Is the attatched ER - Diagram circular?

    Hello,

    I am currently working on a student project meant to help small IT companies track their hardware and software assets. I have composed an ER Diagram and before I get too much further I was wondering if someone could tell me whether or not is contains an invalid circular reference. Please see the attached picture of the ER Diagram.

    Thanks in advance,

    McKelly
    Attached Thumbnails Attached Thumbnails er_diag_assets_1.1.PNG  

  2. #2
    Join Date
    May 2005
    Location
    San Antonio, Texas
    Posts
    134
    I think you could load all the tables and get no complaints from the database. All foreign keys would be valid if you loaded them in the right order and you wouldn't get mutually dependent references. Thats an easy way for me to check for wonky references :P

    I assumed the hardware_platform would be a foreign key reference in system in the 1 to 1 relationship.
    I created link tables below where the many to many relationships exist:
    table load order:
    client
    platform_type
    platform_status
    hardware_platform
    users
    system
    software_type
    software
    system_software
    client_software

    I have a feeling that there may be to many references though for the problem. It just seems very restrictive, but I can't really ofter a good opinion on that unless I saw the problem.
    Vi veri veniversum vivus vici
    By the power of truth, I, a living man, have conquered the universe

  3. #3
    Join Date
    Jun 2003
    Location
    Ohio
    Posts
    12,592
    Your diagram looks very pretty, but I find it more useful to arrange ERDs so that one-to-many relationships flow from left to right across the page. This can help illustrate relational integrity issues and is more intuitive than having to check the endpoints of each relationships in order to determine its direction.
    If it's not practically useful, then it's practically useless.

    blindman
    www.chess.com: "sqlblindman"
    www.LobsterShot.blogspot.com

  4. #4
    Join Date
    Nov 2007
    Posts
    9
    Thanks for the feedback. I will see if I can find a way to rearrange the diagram so that the one-to-many relationships flow from left to right. I have implemented the database and all of the keys/foreign constraints as well as the join tables that amthomas mentioned (ClientSoftware and SystemSoftware). I am still concerned that the layout maybe circular however.

  5. #5
    Join Date
    May 2005
    Location
    San Antonio, Texas
    Posts
    134
    For assistance with that you would have to give a description of what you are trying to store. All I can really see is a bunch of abstract entities with not much meaning behind them. I could start guessing at their purpose but I think that would just lead to confusion

    It is a school project though so people probably won't tell you what they think you should do outright good luck!
    Vi veri veniversum vivus vici
    By the power of truth, I, a living man, have conquered the universe

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