A unique identifier (UID) is an

identifier An identifier is a name that identifies (that is, labels the identity of) either a unique object or a unique ''class'' of objects, where the "object" or class may be an idea, physical countable object (or class thereof), or physical noncountable ...

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 Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to practical disciplines (includin ...

and

information system An information system (IS) is a formal, sociotechnical, organizational system designed to collect, process, store, and distribute information. From a sociotechnical perspective, information systems are composed by four components: task, people ...

s. In general, it was associated with an atomic data type. In

relational database A relational database is a (most commonly digital) database based on the relational model of data, as proposed by E. F. Codd in 1970. A system used to maintain relational databases is a relational database management system (RDBMS). Many relatio ...

s, certain attributes of an

entity An entity is something that exists as itself, as a subject or as an object, actually or potentially, concretely or abstractly, physically or not. It need not be of material existence. In particular, abstractions and legal fictions are usually r ...

that serve as unique identifiers are called

primary key In the relational model of databases, a primary key is a ''specific choice'' of a ''minimal'' set of attributes (columns) that uniquely specify a tuple (row) in a relation ( table). Informally, a primary key is "which attributes identify a record ...

s. In mathematics,

set theory Set theory is the branch of mathematical logic that studies sets, which can be informally described as collections of objects. Although objects of any kind can be collected into a set, set theory, as a branch of mathematics, is mostly concer ...

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: # serial numbers, assigned incrementally or sequentially, by a central authority or accepted reference. # 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 informal use of language, still referred to as "unique" ##

Hash function A hash function is any function that can be used to map data of arbitrary size to fixed-size values. The values returned by a hash function are called ''hash values'', ''hash codes'', ''digests'', or simply ''hashes''. The values are usually ...

s: based on the content of the identified object, ensuring that equivalent objects use the same UID. ##

Random number generator Random number generation is a process by which, often by means of a random number generator (RNG), a sequence of numbers or symbols that cannot be reasonably predicted better than by random chance is generated. This means that the particular outc ...

: based on random process. # names or codes allocated by choice which are forced to be unique by keeping a central registry such as the EPC Information Services. # names or codes allocated using a regime involving multiple (concurrent) issuers of unique identifiers that are each assigned mutually exclusive partitions of a global address space such that the unique identifiers assigned by each issuer in each exclusive address space partition are guaranteed to be globally unique. Examples include (1) the media access control address

MAC address A media access control address (MAC address) is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment. This use is common in most IEEE 802 networking tec ...

uniquely assigned to each individual hardware network interface device produced by the manufacturer of the devices, (2) consumer product bar codes assigned to products using identifiers assigned by manufacturers that participate in GS1 identification standards, and (3) the unique and persistent Legal Entity Identifier assigned to a legal entity by one of the LEI registrars in the Global Legal Entity Identifier System (GLEIS) managed by the Global LEI Foundation (GLEIF). 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

* Electronic Identifier Serial Publication (EISP) * Electronic Product Code (EPC) *

International eBook Identifier Number International is an adjective (also used as a noun) meaning "between nations". International may also refer to: Music Albums * ''International'' (Kevin Michael album), 2011 * ''International'' (New Order album), 2002 * ''International'' (The T ...

(IEIN) *

International Standard Book Number The International Standard Book Number (ISBN) is a numeric commercial book identifier that is intended to be unique. Publishers purchase ISBNs from an affiliate of the International ISBN Agency. An ISBN is assigned to each separate edition and ...

(ISBN) *

National identification number A national identification number, national identity number, or national insurance number or JMBG/EMBG is used by the governments of many countries as a means of tracking their citizens, permanent residents, and temporary residents for the purpo ...

* Part number * Radio

call sign In broadcasting and radio communications, a call sign (also known as a call name or call letters—and historically as a call signal—or abbreviated as a call) is a unique identifier for a transmitter station. A call sign can be formally assig ...

s *

Stock keeping unit In inventory management, a stock keeping unit (abbreviated as SKU and pronounced or ) is the unit of measure in which the stocks of a material are managed. Or to put it another way; is a distinct type of item for sale, purchased, or tracked in ...

(SKU) * Track and trace

National identification number

National identification number is used by the

government A government is the system or group of people governing an organized community, generally a state. In the case of its broad associative definition, government normally consists of legislature, executive, and judiciary. Government ...

s of many countries as a means of tracking their

citizen Citizenship is a "relationship between an individual and a state to which the individual owes allegiance and in turn is entitled to its protection". Each state determines the conditions under which it will recognize persons as its citizens, and ...

permanent resident Permanent residency is a person's legal resident status in a country or territory of which such person is not a citizen but where they have the right to reside on a permanent basis. This is usually for a permanent period; a person with suc ...

s, and temporary residents for the purposes of work,

taxation A tax is a compulsory financial charge or some other type of levy imposed on a taxpayer (an individual or legal entity) by a governmental organization in order to fund government spending and various public expenditures (regional, local, o ...

, government

benefits Benefit or benefits may refer to: Arts, entertainment and media * ''Benefit'' (album), by Jethro Tull, 1970 * "Benefits" (''How I Met Your Mother''), a 2009 TV episode * '' The Benefit'', a 2012 Egyptian action film Businesses and organisatio ...

health care Health care or healthcare is the improvement of health via the prevention, diagnosis, treatment, amelioration or cure of disease, illness, injury, and other physical and mental impairments in people. Health care is delivered by health ...

, and other governance-related functions.

Chemistry

CAS registry number A CAS Registry Number (also referred to as CAS RN or informally CAS Number) is a unique identification number assigned by the Chemical Abstracts Service (CAS), US to every chemical substance described in the open scientific literature. It inclu ...

* IUPAC nomenclature

Computing

* Cryptographic hashes * Identity correlation *

* Object identifier (OID) * Organizationally unique identifier (OUI) * Universally unique identifier (UUID) or globally unique identifier (GUID) *

World Wide Port Name In computing, a World Wide Port Name, WWPN, or WWpN, is a World Wide Name assigned to a port in a Fibre Channel fabric. Used on storage area networks, it performs a function equivalent to the MAC address in Ethernet protocol, as it is supposed t ...

Economics, tax and regulation

Harmonized System The Harmonized Commodity Description and Coding System, also known as the Harmonized System (HS) of tariff nomenclature is an internationally standardized system of names and numbers to classify traded products. It came into effect in 1988 and has ...

* Payment card number * Unique Transaction Identifier (UTI) *

Universal Product Code The Universal Product Code (UPC or UPC code) is a barcode symbology that is widely used worldwide for tracking trade items in stores. UPC (technically refers to UPC-A) consists of 12 digits that are uniquely assigned to each trade item. Along w ...

Internet architecture and standards

* Best Current Practice (BCP) *

For Your Information "FYI" is a common abbreviation of "for your information" (or "for your interest"). "FYI" is commonly used in email, instant messaging and other messages to indicate an informational message, with an intent to communicate to the receiver that they ...

(FYI) * Internet Draft (I-D) *

Internet Experiment Note An Internet Experiment Note (IEN) is a sequentially numbered document in a series of technical publications issued by the participants of the early development work groups that created the precursors of the modern Internet. After DARPA began the ...

(IEN) * Internet Standard (STD) *

Request for Comments A Request for Comments (RFC) is a publication in a series from the principal technical development and standards-setting bodies for the Internet, most prominently the Internet Engineering Task Force (IETF). An RFC is authored by individuals or ...

(RFC) * RARE Technical Reports (RTR)

Legal

* Bates numbering * European Case Law Identifier (ECLI) * Gun serial number * Legal Entity Identifier (LEI) * Lex (URN)

Mathematical publications

Mathematical Reviews ''Mathematical Reviews'' is a journal published by the American Mathematical Society (AMS) that contains brief synopses, and in some cases evaluations, of many articles in mathematics, statistics, and theoretical computer science. The AMS also ...

number *

Zentralblatt MATH zbMATH Open, formerly Zentralblatt MATH, is a major reviewing service providing reviews and abstracts for articles in pure and applied mathematics, produced by the Berlin office of FIZ Karlsruhe – Leibniz Institute for Information Infrastruct ...

identifier

Research / Science

* Archival resource keys (ARK), with 8.2 billion ARKs issued. *

Digital object identifier A digital object identifier (DOI) is a persistent identifier or handle used to uniquely identify various objects, standardized by the International Organization for Standardization (ISO). DOIs are an implementation of the Handle System; th ...

s (DOI), with 200 million DOIs issued. * Identifiers.org *

ORCID The ORCID (; Open Researcher and Contributor ID) is a nonproprietary alphanumeric code to uniquely identify authors and contributors of scholarly communication as well as ORCID's website and services to look up authors and their bibliographic ...

(Open Researcher and Contributor ID) *

Smithsonian trinomial A Smithsonian trinomial (formally the Smithsonian Institution Trinomial System, abbreviated SITS) is a unique identifier assigned to archaeological sites in many states in the United States. They are composed of one or two digits coding for the sta ...

* Systematic name

Transportation

* American rail transportation Reporting marks * IMO number to identify sea-going ships *

International Air Transport Association airport code An IATA airport code, also known as an IATA location identifier, IATA station code, or simply a location identifier, is a three-character alphanumeric geocode designating many airports and metropolitan areas around the world, defined by the ...

s *

IMO IMO or Imo may refer to: Biology and medicine * Irish Medical Organisation, the main organization for doctors in the Republic of Ireland * Intelligent Medical Objects, a privately held company specializing in medical vocabularies * Isomaltooligos ...

container codes according to

ISO 6346 ISO 6346 is an international standard covering the coding, identification and marking of intermodal (shipping) containers used within containerized intermodal freight transport by the International Organization for Standardization (ISO). T ...

for shipping containers * License plate number * Maritime Mobile Service Identity (MMSI) * UIC wagon numbers

References

{{reflist Names Unique identifiers