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When to use a multidimensional relationship in an ERD? My textbook is in Dutch, and the two paragraphs that explain about multidimensional relationships is too vague and brief. I don't understand when it is applicable to use it, and I can't find any information on this subject on the internet.

My guess is that my textbook is naming the concept different from what it's real name is, since I can't find any information on it. In my textbook it shows the following diagram:

enter image description here

Unfortunately, this is the cardinality notation my textbook and teacher are using, I don't know how it translates to any different notations, but to explain how it works: T = mandatory, O = optionality, n, m, k all mean many.

It works in the opposite direction as most notations: All teachers can teach 0 or many subjects and classes, all subjects are teached 1 to many times by teachers and to classes, all classes are teached 1 to many subjects by 1 to many teachers.

Maybe if someone knows its true name I can do some research on this concept...

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I'm going to share some terminology with you that may help in your research.

The relationship you pictured is what is called a "ternary" relationship. It involves three entities. The simple relationships we usually deal with involve only two entities, and could be called "binary". There are "quaternary" relatinships, and so on. The general term is "n-ary".

You may also want to look up the following: Star schema, Ralph Kimball, Data warehousing, and multidimensional data model. A star schema is basically the intersection of relational tables and multidimensional modeling. There's too much here for me to do the subject justice. Happy hunting!

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  • Haha, that's some very complex stuff, especially data warehousing and multidimensional data models. Do you think knowing about them is a must in order to understand how to model n-ary relationships? – user1534664 Sep 18 '14 at 11:23
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    No, I don't. The only time I needed to understand n-ary relationships was in the context of a star schema. But they can be useful feature of ER modeling with no intent to build a star schema. – Walter Mitty Sep 19 '14 at 11:59

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