In a database the items are often identified by a numer or other form of identifier such as guid which has no strong meaning in itself, but can be used to refer to the item uniquely in other database records or external references such as a URI. In some databases the items are identified by one or more field values, known as the database 'key'; however, this may be fragile, for example if the combination of name and address is used to identify soemone, but they subsequently move.
Used on pages 203, 204
Also known as database id