Every instance of an entity has a unique identifier.  Simple identifiers can be defined as attributes of an entity.  In cases where one or more complex identifiers are required, an object is required. This is implemented using an entity identification specification and its associated entity identification objects.  For example, ANS T1.253 specifies a complex identifier for a network location Figure EI.10 – Entity and Entity Identification below shows an example of the EntityIdentificationSpecification, the EntityIdentification, and the RootEntity instance identified using this specification. (Note that the multiplicity of the RootEntityRecognizedUsing association is 0..1 on the RootEntity side, and not 1, because our first option doesn’t use this approach; therefore, RootEntity and RootEntityType must be kept optional.)<br/>