Unlike a primary key or an alternate key, an inversion entry is an attribute or set of attributes that are commonly used to access an entity, but which may not result in finding exactly one instance of an entity. In a data model, the symbol IEn is placed after the attribute.
For example, in addition to locating information in an employee database using an employee's identification number, a business may want to search by employee name. Often, a name search results in multiple records, which requires an additional step to find the exact record. By assigning an attribute to an inversion entry group, a non-unique index is created in the database.
Note: An attribute can belong to an alternate key group as well as an inversion entry group.
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