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  1. #1
    Join Date
    Oct 2010

    Post Many to 2 relationship ?

    Hi everyone, this is my question
    In an ERD, if there is a Many-to-2 relationship, can we represent it as it is in an ERD (if Chen Notation is considered) or do we have to use it as an Many-to-Many relationship?
    But if we represent it as Many to Many, we have to create an extra table unnecessarily.
    So if I want to stick to creating 2 tables only (in the relational schema), how can we represent it in the ERD.

    EX: - A Basket Bass match has 2 teams to play
    one team can play many matches

  2. #2
    Join Date
    Feb 2004
    One Flump in One Place
    You don't represent the M:M relationship with a table in an ERD, only when implementing it in the database. However, Many:2 is exactly the same as M:M anyway; it is the fact that more than one can relate "more than one" to "more than one" that is the key. In other words, they are different flavours of the same relationship type. Anyhoo, you can define the cardinality in your ERD in either case (though I confess I don't know about Chen notation).

    However, if you are recording participants in a match then I would have these as two attributes in your match entity (home_team, away_team). Apart from anything else here is no way to enforce a mandatory cardinality in any RDBMS I know, but you can ensure the two columns are NOT NULL.
    pootle flump
    ur codings are working excelent.

  3. #3
    Join Date
    Oct 2010


    Earlier I have drawn that (Match and Team) relationship as Many to many in the ERD. Then in the relational schema, I've broke the M:M relationship as 2 One-to-Many relationships. The linking table was named as Participation. But then I got to know that there is a requirement for the match entity to be identified by its (teams playing and match date). So then i decided to put that 2 teams in the same table (match).

    I've implemented it and works fine.

    What I want to know is that how can we represent it in the ERD USing "Chen notation".

    Shall I put many to many in the ERD? I'm quite sure you can't put many to 2 though

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