A unique identifier (UID) is an identifier that is guaranteed to be unique among all identifiers used for those objects and for a specific purpose. The concept was formalized early in the development of computer science and information systems. In general, it was associated with an atomic data type. In relational databases, certain attributes of an entity that serve as unique identifiers are called primary keys. In mathematics, set theory uses the concept of element indices as unique identifiers.

Classification

There are some main types of unique identifiers, each corresponding to a different generation strategy: The above methods can be combined, hierarchically or singly, to create other generation schemes which guarantee uniqueness. In many cases, a single object may have more than one unique identifier, each of which identifies it for a different purpose.

Examples

National identification number

National identification number is used by the governments of many countries as a means of tracking their citizens, permanent residents, and temporary residents for the purposes of work, taxation, government benefits, health care, and other governance-related functions.

Chemistry

Computing

Economics, tax and regulation

Internet architecture and standards

Legal

Mathematical publications

Research / Science

Transportation