![]() ![]() Many years later, please mind the different notations of ER diagrams, the question is thus not precise enough. Some of these are used before building the database. There are many tools that are more sophisticated than MS Access for making diagrams on a larger scale. This will be fairly complete, if the database builder has identified the foreign keys. Perhaps the simplest is the "Relationship Diagram" that MS Access can produce from a completed database. There are many ways to represent a relational model. This junction table contains two or more foreign keys. And a relational model will have an extra table, often called a "junction table" between two entity tables that are linked by a many-to-many relationship. A relational model has the foreign keys included in the tables, and these serve to implement the relationships which the ER model identifies. ![]() Today, more than half of the ER diagrams floating around are really diagrams of a relational model, and not of an ER model. Sometimes, a relationship will be indicated separately by a diamond. The lines have some kind of indicator for cardinality at either end or both ends. The ER model does not use foreign keys to represent relationships. ER Diagrams were originally used only to represent the ER model.
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