Entity Relationship Diagram

After normalisation, a database is likely to have a series of different tables which have to link together to make the database function efficiently. An Entity Relationship (E/R) diagram is used to map put these links from table to table.
The E/R diagram matches primary keys to foreign keys, and displays the cardinality of the relationships that are displayed as 1:1, 1:M. (In the case of an unnormalised system it could be possible to display a M:N (many to many) relationship).

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