A unique identifier (UID) is an identifier 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 (includi ...

and information systems. 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 ...

that serve as unique identifiers are called primary keys. In mathematics, set theory 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 EPC may refer to: Government and politics * Eastern Provincial Council, in Sri Lanka * European Policy Centre, a Belgian think tank * European Political Community (1952), a former political organization proposed in 1952 * European Political Comm ...

. # 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 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), ''Electronics'' (magazine), a defunct American trade journal *Electronic storage, the storage of data using an electroni ...

(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 (IEIN) * International Standard Book Number (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 purp ...

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 signs * Stock keeping unit (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 is ...

s of many countries as a means of tracking their citizens,

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, government benefits, health care, and other governance-related functions.

Chemistry

* CAS registry number *

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). T ...

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 ...

* MAC address *

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 le ...

(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, u ...

(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 situat ...

* 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 wi ...

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 publish ...

(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 the ...

(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 (RFC) * RARE Technical Reports (RTR)

Legal

* Bates numbering *

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 standard ...

(ECLI) * Gun serial number * 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 number * Zentralblatt MATH identifier

Research / Science

Archival resource key An Archival Resource Key (ARK) is a multi-purpose URL suited to being a persistent identifier for information objects of any type. It is widely used by libraries, data centers, archives, museums, publishers, and government agencies to provide re ...

s (ARK), with 8.2 billion ARKs issued. * Digital object identifiers (DOI), with 200 million DOIs issued. *

Identifiers.org Identifiers.org is a project providing stable and perennial identifiers for data records used in the Life Sciences. The identifiers are provided in the form of Uniform Resource Identifiers (URIs). Identifiers.org is also a resolving system, that r ...

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 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). The ...

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). ...

(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