Associative entity

An associative entity is a term used in relational and entity–relationship theory.

A base relation representing this kind of entity is called, informally, an associative table.

In effect, it contains a number of foreign keys (FK), each in a many-to-one relationship from the junction table to the individual data tables.

The PK of the associative table is typically composed of the FK columns themselves.

An example of the practical use of an associative table would be to assign permissions to users.