An MPI is generally used to manage patient identification numbers and cross-reference them across disparate systems. Healthcare organizations may have several systems handling various different data processing needs, from laboratory to billing, or from ADT to Image Manager. For example, each system may have its own person database and its own person identifier numbering schemes. Even the same type of system may be used to manage tasks at different “entities”, i.e.,between two enterprises that may have distinguished historical Patient IDs. Each of these can be called an ID Domain.