[1] The concept was formalized early in the development of computer science and information systems.
In relational databases, certain attributes of an entity that serve as unique identifiers are called primary keys.
[2] In mathematics, set theory uses the concept of element indices as unique identifiers.
There are some main types of unique identifiers,[1] each corresponding to a different generation strategy: The above methods can be combined, hierarchically or singly, to create other generation schemes which guarantee uniqueness.
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.