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Relational database management systems can’t have M:M relationships, so before converting a data model to a database in Access, SQL Server, mysql, or other relational DBMS, the data modeler must solve the M:M into something else.

when drawing the er diagrams what is the correct option regrading many to many relationships ?

  • solve many to many relationship in er diagram
  • keep many to many relationship to solve when doing physical data modeling(before normalizing the database).
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  • ? use a cross reference table
    – Ewan
    Oct 12, 2017 at 10:14
  • @Ewan - That was the question. Should one always use cross-reference tables in an ER diagram, or can one stick with many-to-many relationship symbol?
    – Vladimir Stokic
    Oct 12, 2017 at 10:18
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    oh i see! depends on the intended audience i think
    – Ewan
    Oct 12, 2017 at 10:20

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I think this is a judgment call.

My opinion is that, if we have strictly cross-reference table (table consisting only of FKs to two tables), then leave it as a many-to-many relationship for the sake of diagram simplicity. After all, it is an ER (entity-relationship) diagram, and people should focus on just that.

However, if you have any additional columns, then you have to solve the relationship in the ER diagram.

One could argue that solving the ER diagram in all cases improves consistency of the diagram, and they would be right. However, it also increases the complexity of the diagram. So, you can go either way, depending on your personal preferences.

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  • This is what I would go with, in the case of ER diagram.
    – Nasik Shafeek
    Oct 18, 2017 at 15:03

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