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, person, physical countable object (or class thereof), or physical mass ...

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, information, and automation. Computer science spans Theoretical computer science, theoretical disciplines (such as algorithms, theory of computation, and information theory) to Applied science, ...

and

information system An information system (IS) is a formal, sociotechnical, organizational system designed to collect, process, Information Processing and Management, store, and information distribution, distribute information. From a sociotechnical perspective, info ...

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

relational database A relational database (RDB) is a database based on the relational model of data, as proposed by E. F. Codd in 1970. A Relational Database Management System (RDBMS) is a type of database management system that stores data in a structured for ...

s, certain attributes of an

entity An entity is something that Existence, exists as itself. It does not need to be of material existence. In particular, abstractions and legal fictions are usually regarded as entities. In general, there is also no presumption that an entity is Lif ...

that serve as unique identifiers are called ''

primary key In the relational model of databases, a primary key is a designated attribute (column) that can reliably identify and distinguish between each individual record in a table. The database creator can choose an existing unique attribute or combinati ...

s''. In mathematics,

set theory Set theory is the branch of mathematical logic that studies Set (mathematics), 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 mathema ...

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 number A serial number (SN) is a unique identifier used to ''uniquely'' identify an item, and is usually assigned incrementally or sequentially. Despite being called serial "numbers", they do not need to be strictly numerical and may contain letters ...

s, 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 (mathematics), function that can be used to map data (computing), data of arbitrary size to fixed-size values, though there are some hash functions that support variable-length output. The values returned by a ...

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 is generated that cannot be reasonably predicted better than by random chance. This means that the particular ou ...

: 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 MAC address (short for medium access control address or media access control 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 i ...

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 The Legal Entity Identifier (LEI) is a unique global identifier for legal entities participating in financial transactions. Also known as an LEI code or LEI number, its purpose is to help identify legal entities on a globally accessible database. L ...

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 The Electronic Product Code (EPC) is designed as a universal identifier (using an idiosyncratic numerical code for each different commodity) that provides a unique identity for every physical object anywhere in the world, for all time. The EPC s ...

(EPC) * International eBook Identifier Number (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 or receive ISBNs from an affiliate of the International ISBN Agency. A different ISBN is assigned to e ...

(ISBN) *

National identification number A national identification number or national identity number is used by the governments of many countries as a means of uniquely identifying their citizens or residents for the purposes of work, taxation, government benefits, health care, bank ...

Amazon Standard Identification number An Amazon Standard Identification Number (ASIN) is a 10-character alphanumeric unique identifier assigned by Amazon.com and its partners for product identification within the Amazon organization. They were designed in 1996 by Rebecca Allen, an A ...

Part number A part number (often abbreviated PN, P/N, part no., or part #) is an identifier of a particular part design or material used in a particular industry. Its purpose is to simplify reference that item. A part number unambiguously identifies a part ...

* 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 as ...

s *

Stock keeping unit In inventory management, a stock keeping unit (abbreviated as SKU, pronounced or ) is the unit of measure in which the stocks of a material are managed. It is a distinct type of item for sale, purchase, or tracking in inventory, such as a produ ...

(SKU) *

Track and trace In the distribution and logistics of many types of products, track and trace or tracking and tracing concerns a process of determining the current and past locations (and other information) of a unique item or property. Mass serialization is t ...

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 (polity), state. In the case of its broad associative definition, government normally consists of legislature, executive (government), execu ...

s of many countries as a means of tracking their

citizen Citizenship is a membership and allegiance to a sovereign state. Though citizenship is often conflated with nationality in today's English-speaking world, international law does not usually use the term ''citizenship'' to refer to nationality ...

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 such l ...

s, and temporary residents for the purposes of work,

taxation A tax is a mandatory financial charge or levy imposed on an individual or legal person, legal entity by a governmental organization to support government spending and public expenditures collectively or to Pigouvian tax, regulate and reduce nega ...

, government benefits,

health care Health care, or healthcare, is the improvement or maintenance of health via the preventive healthcare, prevention, diagnosis, therapy, treatment, wikt:amelioration, amelioration or cure of disease, illness, injury, and other disability, physic ...

, and other governance-related functions.

Chemistry

* CAS registry number *

IUPAC nomenclature IUPAC nomenclature is a set of recommendations for naming chemical compounds and for describing chemistry and biochemistry in general. The International Union of Pure and Applied Chemistry (IUPAC) is the international authority on chemical nomenc ...

Computing

* Cryptographic hashes * Identity correlation *

Object identifier In computing, object identifiers or OIDs are an identifier mechanism standardized by the International Telecommunication Union (ITU) and ISO/IEC for naming any object, concept, or "thing" with a globally unambiguous persistent name. Syntax and lex ...

(OID) *

Organizationally unique identifier An organizationally unique identifier (OUI) is a 24-bit number that uniquely identifies a vendor, manufacturer, or other organization. OUIs are purchased from the Institute of Electrical and Electronics Engineers (IEEE) Registration Authority ...

(OUI) *

Universally unique identifier A Universally Unique Identifier (UUID) is a 128-bit label used to uniquely identify objects in computer systems. The term Globally Unique Identifier (GUID) is also used, mostly in Microsoft systems. When generated according to the standard methods ...

(UUID) or globally unique identifier (GUID) * World Wide Port Name

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 ha ...

Payment card number A payment card number, primary account number (PAN), or simply a card number, is the card identifier found on payment cards, such as credit cards and debit cards, as well as stored-value cards, gift cards and other similar cards. In some situat ...

* Unique Transaction Identifier (UTI) *

Universal Product Code The Universal Product Code (UPC or UPC code) is a barcode#Symbologies, barcode symbology that is used worldwide for tracking trade items in stores. The chosen symbology has bars (or spaces) of exactly 1, 2, 3, or 4 units wide each; each decimal ...

Internet architecture and standards

Best Current Practice A best current practice, abbreviated as BCP, is a ''de facto'' level of performance in engineering and information technology. It is more flexible than a standard, since techniques and tools are continually evolving. The Internet Engineering Tas ...

(BCP) * For Your Information (FYI) *

Internet Draft An Internet Draft (I-D) is a document published by the Internet Engineering Task Force (IETF) containing preliminary technical specifications, results of networking-related research, or other technical information. Often, Internet Drafts are int ...

(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. History After DARPA be ...

(IEN) *

Internet Standard In computer network engineering, an Internet Standard is a normative specification of a technology or methodology applicable to the Internet. Internet Standards are created and published by the Internet Engineering Task Force (IETF). They allow ...

(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 Bates numbering (also known as Bates stamping, Bates branding, Bates coding or Bates labeling) is a method of sequentially Pagination, numbering pages with a reference number. A hand-operated Bates numbering device is used to "stamp" a number on ...

European Case Law Identifier The European Case Law Identifier (ECLI) is an identifier for court decisions in Europe. The identifier consists of five elements separated by colons: ECLI:'' ountry code':'' ourt identifier':'' ear of decision':'' pecific identifier'. The standa ...

(ECLI) * Gun serial number *

(LEI) *

Lex (URN) is a ''URN namespace'', a type of Uniform Resource Name (URN), that allows accurate identification of laws and other legal norms. LexML Brazil and Italy (Civil law countries) officially recognize the ''URN LEX standard draft''. Brazil using LEX ...

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 pu ...

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 Infrastru ...

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. This addresses the problem that a particular author's contributions to the scien ...

(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. Trinomials are composed of a one or two digit coding fo ...

Systematic name A systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance, out of a specific population or collection. Systematic names are usually part of a nomenclature. A semisystematic name or semitrivi ...

Transportation

* American rail transportation

Reporting marks Reporting may refer to * any activity that leads to reports * in particular business reporting * Data reporting * Sustainability reporting * Financial reporting * international reporting of financial information for tax purposes under the OECD's ...

IMO number The IMO number of the International Maritime Organization is a generic term with two distinct applications: * the IMO ship identification number is a unique ship identifier; or, * the IMO company and registered owner identification number is u ...

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 unique three-letter geocode designating many airports, cities (with one or more airports) and metropolitan areas (cit ...

s * IMO 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). The ...

for shipping containers *

License plate A vehicle registration plate, also known as a number plate (British, Indian and Australian English), license plate (American English) or licence plate (Canadian English), is a metal or plastic plate attached to a motor vehicle or trailer for ...

number * Maritime Mobile Service Identity (MMSI) * UIC wagon numbers

References

{{reflist Names