Unique identifier

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With reference to a given (possibly implicit) set of objects, a unique identifier (UID) is any identifier which is guaranteed to be unique among all identifiers used for those objects and for a specific purpose. There are three main types of unique identifiers, each corresponding to a different generation strategy:

  • serial numbers, assigned incrementally or sequentially
  • random numbers, selected from a number space much larger than the maximum (or expected) number of objects to be identified. Although not really unique, some identifiers of this type may be appropriate for identifying objects in many practical applications and are, with abuse of language, still referred to as "unique"
  • names or codes allocated by choice which are forced to be unique by keeping a central registry such as the EPC Information Services.

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.

In relational databases, certain attributes of an entity that serve as unique identifiers are called primary keys.


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.

Aadhaar, the UID of India

Aadhaar is a 12-digit national identification number assigned to residents of India for lifetime. Its format is 1234-5678-9012 where the 11-digits are used as a sequence number and the rightmost 1-digit as an error detection check-sum digit. Aadhaar Number (AN) is not a proof of citizenship. It only guarantees identity; not rights, benefits or entitlements. Unique Identification Authority of India (UIDAI), a government agency, is the Registrar of Identities. It was established in January 2009 and commenced assigning AN from September 2010.[1]

As of April 2015, 814,495,057 AN have been assigned. In July 2014, this figure was 641,932,798. In September 2013, it was 416,992,803.[2]

Aadhaar is a digital identity, instantly verifiable online at the point of service (PoS), at any time, in a paperless way. The government hopes that it will enable under-privileged people to access social security benefits, which they have been deprived so far due to lack of proper identity.[3]




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