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 databases, 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 re ...

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 number A serial number is a unique identifier assigned incrementally or sequentially to an item, to ''uniquely'' identify it. Serial numbers need not be strictly numerical. They may contain letters and other typographical symbols, or may consist ent ...

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 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 techno ...

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 Electronic may refer to: *Electronics, the science of how to control electric energy in semiconductor * ''Electronics'' (magazine), a defunct American trade journal *Electronic storage, the storage of data using an electronic device *Electronic co ...

(EISP) *

Electronic Product Code The Electronic Product Code (EPC) is designed as a universal identifier (using a 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 stru ...

(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 an ...

(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 purpos ...

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 to 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 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 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. This concept can be s ...

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 i ...

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 ...

s, permanent residents, 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, or ...

, government benefits,

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 pr ...

, 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 A chemical nomenclature is a set of rules to generate systematic names for chemical compounds. The nomenclature used most frequently worldwide is the one created and developed by the International Union of Pure and Applied Chemistry (IUPAC). The ...

Computing

* Cryptographic hashes *

Identity correlation In information systems, identity correlation is a process that reconciles and validates the proper ownership of disparate user account login IDs ( user names) that reside on systems and applications throughout an organization and can permanently li ...

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 l ...

(OID) * Organizationally unique identifier (OUI) *

Universally unique identifier A universally unique identifier (UUID) is a 128-bit label used for information in computer systems. The term globally unique identifier (GUID) is also used. When generated according to the standard methods, UUIDs are, for practical purposes, uni ...

(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 has ...

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 situatio ...

Unique Transaction Identifier A Unique Transaction Identifier (Acronym: UTI), alternatively called Unique Swap Identifier (Acronym: USI) is a globally unique identifier for individual transactions in financial markets. USIs were introduced in late 2012 in the U.S. in the contex ...

(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 ...

Internet architecture and standards

Best Current Practice A Best Current Practice (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 Task Force publishe ...

(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. After DARPA began the ...

(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 g ...

(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 numbering pages with a reference number. A hand-operated Bates numbering device is used to "stamp" a number on a page, and ...

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 standar ...

(ECLI) *

Gun serial number A gun serial number is a unique identifier assigned to a singular firearm. There is no international uniformity in gun serial numbers. Besides a widespread numerical base, they may contain letters and other typographical symbols, or may consis ...

* Legal Entity Identifier (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) already officially recognize the ''URN LEX standard draft v0.9'', as ...

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 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; they a ...

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 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 semitrivial ...

Transportation

* American rail transportation

Reporting marks A reporting mark is a code used to identify owners or lessees of rolling stock and other equipment used on certain rail transport networks. The code typically reflects the name or identifying number of the owner, lessee, or operator of the equip ...

IMO number The IMO number of the International Maritime Organization is a generic term covering two distinct meanings. The IMO ship identification number, is a type of hull number used as a unique ship identifier, and the IMO company and registered owne ...

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 I ...

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). T ...

for shipping containers *

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

number *

Maritime Mobile Service Identity A Maritime Mobile Service Identity (MMSI) is effectively a maritime object's international ''maritime telephone number'', a temporarily assigned UID, issued by that object's current flag state, (unlike an IMO, which is a global forever UID). An ...

(MMSI) *

UIC wagon numbers Wagon numbers (or coach numbers) are key data for railway operations. They enable a railway wagon or coach to be positively identified and form a common language between railway operators, infrastructure companies and the state authorities. The ...

References

{{reflist Names Unique identifiers