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] substance (or class thereof). The abbreviation ID often refers to identity, identification (the process of identifying), or an identifier (that is, an instance of identification). An identifier may be a word, number, letter, symbol, or any combination of those.

The words, numbers, letters, or symbols may follow an encoding system (wherein letters, digits, words, or symbols stand for (represent) ideas or longer names) or they may simply be arbitrary. When an identifier follows an encoding system, it is often referred to as a code or ID code. For instance the ISO/IEC 11179 metadata registry standard defines a code as system of valid symbols that substitute for longer values in contrast to identifiers without symbolic meaning. Identifiers that do not follow any encoding scheme are often said to be arbitrary IDs; they are arbitrarily assigned and have no greater meaning. (Sometimes identifiers are called "codes" even when they are actually arbitrary, whether because the speaker believes that they have deeper meaning or simply because they are speaking casually and imprecisely.)

The unique identifier (UID) is an identifier that refers to only one instance—only one particular object in the universe. A part number is an identifier, but it is not a unique identifier—for that, a serial number is needed, to identify each instance of the part design. Thus the identifier "Model T" identifies the class (model) of automobiles that Ford's Model T comprises; whereas the unique identifier "Model T Serial Number 159,862" identifies one specific member of that class—that is, one particular Model T car, owned by one specific person.

The concepts of name and identifier are denotatively equal, and the terms are thus denotatively synonymous; but they are not always connotatively synonymous, because code names and ID numbers are often connotatively distinguished from names in the sense of traditional natural language naming. For example, both "Jamie Zawinski" and "Netscape employee number 20" are identifiers for the same specific human being; but normal English-language connotation may consider "Jamie Zawinski" a "name" and not an "identifier", whereas it considers "Netscape employee number 20" an "identifier" but not a "name". This is an emic indistinction rather than an etic one.

Louvre identifiers Ma1274-MR242
Identifiers on the back of a statue in the Louvre


In metadata, an identifier is a language-independent label, sign or token that uniquely identifies an object within an identification scheme. The suffix identifier is also used as a representation term when naming a data element.

ID codes may inherently carry metadata along with them. For example, when you know that the food package in front of you has the identifier "2011-09-25T15:42Z-MFR5-P02-243-45", you not only have that data, you also have the metadata that tells you that it was packaged on September 25, 2011, at 3:42pm UTC, manufactured by Licensed Vendor Number 5, at the Peoria, IL, USA plant, in Building 2, and was the 243rd package off the line in that shift, and was inspected by Inspector Number 45.

Arbitrary identifiers might lack metadata. For example, if a food package just says 100054678214, its ID may not tell anything except identity—no date, manufacturer name, production sequence rank, or inspector number. In some cases, arbitrary identifiers such as sequential serial numbers leak information (i.e. the German tank problem). Opaque identifiers—identifiers designed to avoid leaking even that small amount of information—include "really opaque pointers" and Version 4 UUIDs.

In computer science

In computer science, identifiers (IDs) are lexical tokens that name entities. Identifiers are used extensively in virtually all information processing systems. Identifying entities makes it possible to refer to them, which is essential for any kind of symbolic processing.

In computer languages

In computer languages, identifiers are tokens (also called symbols) which name language entities. Some of the kinds of entities an identifier might denote include variables, types, labels, subroutines, and packages.

Which character sequences constitute identifiers depends on the lexical grammar of the language. A common rule is alphanumeric sequences, with underscore also allowed, and with the condition that it not begin with a digit (to simplify lexing by avoiding confusing with integer literals) – so foo, foo1, foo_bar, _foo are allowed, but 1foo is not – this is the definition used in earlier versions of C and C++, Python, and many other languages. Later versions of these languages, along with many other modern languages, support almost all Unicode characters in an identifier. However, a common restriction is not to permit whitespace characters and language operators; this simplifies tokenization by making it free-form and context-free. For example, forbidding + in identifiers due to its use as a binary operation means that a+b and a + b can be tokenized the same, while if it were allowed, a+b would be an identifier, not an addition. Whitespace in identifier is particularly problematic, as if spaces are allowed in identifiers, then a clause such as if rainy day then 1 is legal, with rainy day as an identifier, but tokenizing this requires the phrasal context of being in the condition of an if clause. Some languages do allow spaces in identifiers, however, such as ALGOL 68 and some ALGOL variants – for example, the following is a valid statement: real half pi; which could be entered as .real. half pi; (keywords are represented in boldface, concretely via stropping). In ALGOL this was possible because keywords are syntactically differentiated, so there is no risk of collision or ambiguity, spaces are eliminated during the line reconstruction phase, and the source was processed via scannerless parsing, so lexing could be context-sensitive.

In most languages, some character sequences have the lexical form of an identifier but are known as keywords – for example, if is frequently a keyword for an if clause, but lexically is of the same form as ig or foo namely a sequence of letters. This overlap can be handled in various ways: these may be forbidden from being identifiers – which simplifies tokenization and parsing – in which case they are reserved words; they may both be allowed but distinguished in other ways, such as via stropping; or keyword sequences may be allowed as identifiers and which sense is determined from context, which requires a context-sensitive lexer. Non-keywords may also be reserved words (forbidden as identifiers), particularly for forward compatibility, in case a word may become a keyword in future. In a few languages, e.g., PL/1, the distinction is not clear.

The scope, or accessibility within a program of an identifier can be either local or global. A global identifier is declared outside of functions and is available throughout the program. A local identifier is declared within a specific function and only available within that function.[1]

For implementations of programming languages that are using a compiler, identifiers are often only compile time entities. That is, at runtime the compiled program contains references to memory addresses and offsets rather than the textual identifier tokens (these memory addresses, or offsets, having been assigned by the compiler to each identifier).

In languages that support reflection, such as interactive evaluation of source code (using an interpreter or an incremental compiler), identifiers are also runtime entities, sometimes even as first-class objects that can be freely manipulated and evaluated. In Lisp, these are called symbols.

Compilers and interpreters do not usually assign any semantic meaning to an identifier based on the actual character sequence used. However, there are exceptions.

For example:

  • In Perl a variable is indicated using a prefix called a sigil, which specifies aspects of how the variable is interpreted in expressions.
  • In Ruby a variable is automatically considered immutable if its identifier starts with a capital letter.
  • In Fortran, the first letter in a variable's name indicates whether by default it is created as an integer or floating point variable.
  • In Go, the capitalization of the first letter of a variable's name determines its visibility (uppercase for public, lowercase for private).

In some languages such as Go, identifiers uniqueness is based on their spelling and their visibility.[2]

In HTML an identifier is one of the possible attributes of an HTML element. It is unique within the document.


Identifiers (IDs) versus Unique identifiers (UIDs)

Many resources may carry multiple identifiers. Typical examples are:

  • One person with multiple names, nicknames, and forms of address (titles, salutations)
    • For example: One specific person may be identified by all of the following identifiers: Jane Smith; Jane Elizabeth Meredith Smith; Jane E. M. Smith; Jane E. Smith; Janie Smith; Janie; Little Janie (as opposed to her mother or sister or cousin, Big Janie); Aunt Jane; Auntie Janie; Mom; Grandmom; Nana; Kelly's mother; Billy's grandmother; Ms. Smith; Dr. Smith; Jane E. Smith, PhD; and Fuzzy (her jocular nickname at work).
  • One document with multiple versions[3]
  • One substance with multiple names (for example, CAS index names versus IUPAC names;[4] INN generic drug names versus USAN generic drug names versus brand names)

The inverse is also possible, where multiple resources are represented with the same identifier (discussed below).

Implicit context and namespace conflicts

Many codes and nomenclatural systems originate within a small namespace. Over the years, some of them bleed into larger namespaces (as people interact in ways they formerly hadn't, e.g., cross-border trade, scientific collaboration, military alliance, and general cultural interconnection or assimilation). When such dissemination happens, the limitations of the original naming convention, which had formerly been latent and moot, become painfully apparent, often necessitating retronymy, synonymity, translation/transcoding, and so on. Such limitations generally accompany the shift away from the original context to the broader one. Typically the system shows implicit context (context was formerly assumed, and narrow), lack of capacity (e.g., low number of possible IDs, reflecting the outmoded narrow context), lack of extensibility (no features defined and reserved against future needs), and lack of specificity and disambiguating capability (related to the context shift, where longstanding uniqueness encounters novel nonuniqueness). Within computer science, this problem is called naming collision. The story of the origination and expansion of the CODEN system provides a good case example in a recent-decades, technical-nomenclature context. The capitalization variations seen with specific designators reveals an instance of this problem occurring in natural languages, where the proper noun/common noun distinction (and its complications) must be dealt with. A universe in which every object had a UID would not need any namespaces, which is to say that it would constitute one gigantic namespace; but human minds could never keep track of, or semantically interrelate, so many UIDs.

Identifiers in various disciplines

Identifier Scope
atomic number, corresponding one-to-one with element name international (via ISV)
Australian Business Number Australian
CAGE code U.S. and NATO
CAS registry number originated in U.S.; today international (via ISV)
CODEN originated in U.S.; today international
Digital object identifier (DOI, doi) Handle System Namespace, international scope
DIN standard number originated in Germany; today international
E number originated in E.U.; may be seen internationally
EC number
Employer Identification Number (EIN) U.S.
Electronic Identifier Serial Publicaction (EISP) international
Global Trade Item Number international
Group identifier many scopes, e.g., specific computer systems
International Chemical Identifier international
International Standard Book Number (ISBN) ISBN is part of the EAN Namespace; international scope
International eBook Identifier Number (IEIN) international
International Standard Serial Number (ISSN) international
ISO standard number, e.g., ISO 8601 international
Library of Congress Control Number U.S., with some international bibliographic usefulness
Personal identification number many scopes, e.g., banks, governments
Personal identification number (Denmark) Denmark
Pharmaceutical code Many different systems
Product batch number
Serial Item and Contribution Identifier U.S., with some international bibliographic usefulness
Serial number many scopes, e.g., company-specific, government-specific
Service batch number
Social Security Number U.S.
Tax file number Australian
Unique Article Identifier (UAI) international

See also


  1. ^ Malik, D. (2014). C++ programming : from problem analysis to program design (7th edition. ed.). Cenage Learning. p. 397. ISBN 978-1-285-85274-4.
  2. ^ "The Go Programming Language Specification - The Go Programming Language". 2013-05-08. Retrieved 2013-06-05.
  3. ^ University of Glasgow. "Procedure for Applying Identifiers to Documents". Retrieved 28 April 2009.
  4. ^ University of Pennsylvania. "Information on Chemical Nomenclature". Retrieved 28 April 2009.

Arginine, also known as L-arginine (symbol Arg or R), is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group, an α-carboxylic acid group, and a side chain consisting of a 3-carbon aliphatic straight chain ending in a guanidino group. At physiological pH, the carboxylic acid is deprotonated (−COO−), the amino group is protonated (−NH3+), and the guanidino group is also protonated to give the guanidinium form (-C-(NH2)2+), making arginine a charged, aliphatic amino acid. It is the precursor for the biosynthesis of nitric oxide. It is encoded by the codons CGU, CGC, CGA, CGG, AGA, and AGG.

In humans, arginine is classified as a semiessential or conditionally essential amino acid, depending on the developmental stage and health status of the individual. Preterm infants are unable to synthesize or create arginine internally, making the amino acid nutritionally essential for them. Most healthy people do not need to supplement with arginine because it is a component of all protein-containing foods and can be synthesized in the body from glutamine via citrulline.


CiNii () is a bibliographic database service for material in Japanese academic libraries, especially focusing on Japanese works and English works published in Japan. The database was founded in April 2005 and is maintained by the National Institute of Informatics. The service searches from within the databases maintained by the NII itself [NII Electronic Library Service (NII-ELS) and Citation Database for Japanese Publications (CJP)], as well as the databases provided by the National Diet Library of Japan, institutional repositories, and other organizations.The database contains more than 15 million articles from more than 3,600 publications. A typical month (in 2012) saw more than 30 million accesses from 2.2 million unique visitors, and is the largest and most comprehensive database of its kind in Japan. Although the database is multidisciplinary, the largest portion of the queries it receives is in the humanities and social sciences field, perhaps because CiNii is the only database that covers Japanese scholarly works in this field (as opposed to the natural, formal, and medical sciences which benefit from other databases).

Digital object identifier

In computing, a Digital Object Identifier or DOI is a persistent identifier or handle used to uniquely identify objects, standardized by the International Organization for Standardization (ISO). An implementation of the Handle System, DOIs are in wide use mainly to identify academic, professional, and government information, such as journal articles, research reports and data sets, and official publications though they also have been used to identify other types of information resources, such as commercial videos.

A DOI aims to be "resolvable", usually to some form of access to the information object to which the DOI refers. This is achieved by binding the DOI to metadata about the object, such as a URL, indicating where the object can be found. Thus, by being actionable and interoperable, a DOI differs from identifiers such as ISBNs and ISRCs which aim only to uniquely identify their referents. The DOI system uses the indecs Content Model for representing metadata.

The DOI for a document remains fixed over the lifetime of the document, whereas its location and other metadata may change. Referring to an online document by its DOI is supposed to provide a more stable link than simply using its URL. But every time a URL changes, the publisher has to update the metadata for the DOI to link to the new URL. It is the publisher's responsibility to update the DOI database. If they fail to do so, the DOI resolves to a dead link leaving the DOI useless.

The developer and administrator of the DOI system is the International DOI Foundation (IDF), which introduced it in 2000. Organizations that meet the contractual obligations of the DOI system and are willing to pay to become a member of the system can assign DOIs. The DOI system is implemented through a federation of registration agencies coordinated by the IDF. By late April 2011 more than 50 million DOI names had been assigned by some 4,000 organizations, and by April 2013 this number had grown to 85 million DOI names assigned through 9,500 organizations.

Geographic Names Information System

The Geographic Names Information System (GNIS) is a database that contains name and locative information about more than two million physical and cultural features located throughout the United States of America and its territories. It is a type of gazetteer. GNIS was developed by the United States Geological Survey in cooperation with the United States Board on Geographic Names (BGN) to promote the standardization of feature names.

The database is part of a system that includes topographic map names and bibliographic references. The names of books and historic maps that confirm the feature or place name are cited. Variant names, alternatives to official federal names for a feature, are also recorded. Each feature receives a permanent, unique feature record identifier, sometimes called the GNIS identifier. The database never removes an entry, "except in cases of obvious duplication."

IATA airport code

An IATA airport code, also known as an IATA location identifier, IATA station code or simply a location identifier, is a three-letter code designating many airports around the world, defined by the International Air Transport Association (IATA). The characters prominently displayed on baggage tags attached at airport check-in desks are an example of a way these codes are used.

The assignment of these codes is governed by IATA Resolution 763, and it is administered by IATA headquarters in Montreal. The codes are published semiannually in the IATA Airline Coding Directory.IATA also provides codes for railway stations and for airport handling entities. A list of airports sorted by IATA code is available. A list of railway station codes, shared in agreements between airlines and rail lines such as Amtrak, SNCF French Railways, and Deutsche Bahn, is available. Many railway administrations have their own list of codes for their stations, such as the list of Amtrak station codes.

ISO 9362

ISO 9362 defines a standard format of Business Identifier Codes (also known as SWIFT-BIC, BIC, SWIFT ID or SWIFT code) approved by the International Organization for Standardization (ISO). It is a unique identification code for both financial and non-financial institutions. The acronym SWIFT stands for the Society for Worldwide Interbank Financial Telecommunication. The ISO has designated SWIFT as the BIC registration authority. When assigned to a non-financial institution, the code may also be known as a Business Entity Identifier or BEI. These codes are used when transferring money between banks, particularly for international wire transfers, and also for the exchange of other messages between banks. The codes can sometimes be found on account statements.

The overlapping issue between ISO 9362 and ISO 13616 is discussed in the article International Bank Account Number (also called IBAN). The SWIFT network does not require a specific format for the transaction so the identification of accounts and transaction types is left to agreements of the transaction partners. In the process of the Single Euro Payments Area the European central banks have agreed on a common format based on IBAN and BIC including an XML-based transmission format for standardized transactions; the TARGET2 is a joint gross clearing system in the European Union that does not require the SWIFT network for transmission (see EBICS). The TARGET-directory lists all the BICs of the banks that are attached to the TARGET2-network being a subset of the SWIFT-directory of BICs.

Integrated Authority File

The Integrated Authority File (German: Gemeinsame Normdatei; also known as the Universal Authority File) or GND is an international authority file for the organisation of personal names, subject headings and corporate bodies from catalogues. It is used mainly for documentation in libraries and increasingly also by archives and museums. The GND is managed by the German National Library (German: Deutsche Nationalbibliothek; DNB) in cooperation with various regional library networks in German-speaking Europe and other partners. The GND falls under the Creative Commons Zero (CC0) licence.The GND specification provides a hierarchy of high-level entities and sub-classes, useful in library classification, and an approach to unambiguous identification of single elements. It also comprises an ontology intended for knowledge representation in the semantic web, available in the RDF format.The Integrated Authority File became operational in April 2012 and integrates the content of the following authority files, which have since been discontinued:

Name Authority File (German: Personennamendatei; PND)

Corporate Bodies Authority File (German: Gemeinsame Körperschaftsdatei; GKD)

Subject Headings Authority File (German: Schlagwortnormdatei; SWD)

Uniform Title File of the Deutsches Musikarchiv (German: Einheitssachtitel-Datei des Deutschen Musikarchivs; DMA-EST)At the time of its introduction on 5 April 2012, the GND held 9,493,860 files, including 2,650,000 personalised names.

International Chemical Identifier

The IUPAC International Chemical Identifier (InChI IN-chee or ING-kee) is a textual identifier for chemical substances, designed to provide a standard way to encode molecular information and to facilitate the search for such information in databases and on the web. Initially developed by IUPAC (International Union of Pure and Applied Chemistry) and NIST (National Institute of Standards and Technology) from 2000 to 2005, the format and algorithms are non-proprietary.

The continuing development of the standard has been supported since 2010 by the not-for-profit InChI Trust, of which IUPAC is a member. The current software version is 1.05 and was released in January 2017.

Prior to 1.04, the software was freely available under the open-source LGPL license,

but it now uses a custom license called IUPAC-InChI Trust License.

International Standard Book Number

The International Standard Book Number (ISBN) is a numeric commercial book identifier which is intended to be unique. Publishers purchase ISBNs from an affiliate of the International ISBN Agency.An ISBN is assigned to each edition and variation (except reprintings) of a book. For example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, and 10 digits long if assigned before 2007. The method of assigning an ISBN is nation-based and varies from country to country, often depending on how large the publishing industry is within a country.

The initial ISBN identification format was devised in 1967, based upon the 9-digit Standard Book Numbering (SBN) created in 1966. The 10-digit ISBN format was developed by the International Organization for Standardization (ISO) and was published in 1970 as international standard ISO 2108 (the SBN code can be converted to a ten-digit ISBN by prefixing it with a zero digit "0").

Privately published books sometimes appear without an ISBN. The International ISBN agency sometimes assigns such books ISBNs on its own initiative.Another identifier, the International Standard Serial Number (ISSN), identifies periodical publications such as magazines and newspapers. The International Standard Music Number (ISMN) covers musical scores.

International Standard Name Identifier

The International Standard Name Identifier (ISNI) is an identifier for uniquely identifying the public identities of contributors to media content such as books, television programmes, and newspaper articles. Such an identifier consists of 16 digits. It can optionally be displayed as divided into four blocks.

ISNI can be used to disambiguate names that might otherwise be confused, and links the data about names that are collected and used in all sectors of the media industries.

It was developed under the auspices of the International Organization for Standardization (ISO) as Draft International Standard 27729; the valid standard was published on 15 March 2012. The ISO technical committee 46, subcommittee 9 (TC 46/SC 9) is responsible for the development of the standard.

International Standard Serial Number

An International Standard Serial Number (ISSN) is an eight-digit serial number used to uniquely identify a serial publication, such as a magazine. The ISSN is especially helpful in distinguishing between serials with the same title. ISSN are used in ordering, cataloging, interlibrary loans, and other practices in connection with serial literature.The ISSN system was first drafted as an International Organization for Standardization (ISO) international standard in 1971 and published as ISO 3297 in 1975. ISO subcommittee TC 46/SC 9 is responsible for maintaining the standard.

When a serial with the same content is published in more than one media type, a different ISSN is assigned to each media type. For example, many serials are published both in print and electronic media. The ISSN system refers to these types as print ISSN (p-ISSN) and electronic ISSN (e-ISSN), respectively. Conversely, as defined in ISO 3297:2007, every serial in the ISSN system is also assigned a linking ISSN (ISSN-L), typically the same as the ISSN assigned to the serial in its first published medium, which links together all ISSNs assigned to the serial in every medium.

Legal Entity Identifier

A Legal Entity Identifier (or LEI) is an international identifier made up of a 20-character identifier that identifies distinct legal entities that engage in financial transactions. It is defined by ISO 17442. Natural persons are not required to have an LEI; they’re eligible to have one issued, however, but only if they act in an independent business capacity. The LEI is a global standard, designed to be non-proprietary data that is freely accessible to all. As of December 2018, over 1,300,000 legal entities from more than 200 countries have now been issued with LEIs.

Location identifier

A location identifier is a symbolic representation for the name and the location of an airport, navigation aid, or weather station, and is used for manned air traffic control facilities in air traffic control, telecommunications, computer programming, weather reports, and related services.

MAC address

A media access control address (MAC address) of a device is a unique identifier assigned to a network interface controller (NIC). For communications within a network segment, it is used as a network address for most IEEE 802 network technologies, including Ethernet, Wi-Fi, and Bluetooth. Within the Open Systems Interconnection (OSI) model, MAC addresses are used in the medium access control protocol sublayer of the data link layer. As typically represented, MAC addresses are recognizable as six groups of two hexadecimal digits, separated by hyphens, colons, or no separator (see Notational conventions below).

A MAC address may be referred to as the burned-in address, and is also known as an Ethernet hardware address, hardware address, and physical address (not to be confused with a memory physical address).

A network node with multiple NICs must have a unique MAC addresses for each. Sophisticated network equipment such as a multilayer switch or router may require one or more permanently assigned MAC addresses.

MAC addresses are most often assigned by the manufacturer of network interface cards. Each is stored in hardware, such as the card's read-only memory or by a firmware mechanism. A MAC address typically includes the manufacturer's organizationally unique identifier (OUI). MAC addresses are formed according to the rules of one of two numbering name spaces managed by the Institute of Electrical and Electronics Engineers (IEEE): EUI-48 (it replaces the obsolete term MAC-48) and EUI-64. EUI is an abbreviation for Extended Unique Identifier.


PubMed is a free search engine accessing primarily the MEDLINE database of references and abstracts on life sciences and biomedical topics. The United States National Library of Medicine (NLM) at the National Institutes of Health maintains the database as part of the Entrez system of information retrieval.From 1971 to 1997, MEDLINE online access to the MEDLARS Online computerized database primarily had been through institutional facilities, such as university libraries. PubMed, first released in January 1996, ushered in the era of private, free, home- and office-based MEDLINE searching. The PubMed system was offered free to the public starting in June 1997.

Request for Comments

In information and communications technology, a Request for Comments (RFC) is a type of publication from the technology community. RFCs may come from many bodies including from the Internet Engineering Task Force (IETF), the Internet Research Task Force (IRTF), the Internet Architecture Board (IAB) or from independent authors. The RFC system is supported by the Internet Society (ISOC).

An RFC is authored by engineers and computer scientists in the form of a memorandum describing methods, behaviors, research, or innovations applicable to the working of the Internet and Internet-connected systems. It is submitted either for peer review or to convey new concepts, information, or (occasionally) engineering humor. The IETF adopts some of the proposals published as RFCs as Internet Standards. However, many RFCs are informational or experimental in nature and are not standards. Request for Comments documents were invented by Steve Crocker in 1969 to help record unofficial notes on the development of ARPANET. RFCs have since become official documents of Internet specifications, communications protocols, procedures, and events.Outside of the Internet community per se, requests for comments have often been published in U.S. Federal government work.


A Uniform Resource Locator (URL), colloquially termed a web address, is a reference to a web resource that specifies its location on a computer network and a mechanism for retrieving it. A URL is a specific type of Uniform Resource Identifier (URI), although many people use the two terms interchangeably. URLs occur most commonly to reference web pages (http), but are also used for file transfer (ftp), email (mailto), database access (JDBC), and many other applications.

Most web browsers display the URL of a web page above the page in an address bar. A typical URL could have the form, which indicates a protocol (http), a hostname (, and a file name (index.html).

Uniform Resource Identifier

A Uniform Resource Identifier (URI) is a string of characters that unambiguously identifies a particular resource. To guarantee uniformity, all URIs follow a predefined set of syntax rules, but also maintain extensibility through a separately defined hierarchical naming scheme (e.g. "http://").

Such identification enables interaction with representations of the resource over a network, typically the World Wide Web, using specific protocols. Schemes specifying a concrete syntax and associated protocols define each URI. The most common form of URI is the Uniform Resource Locator (URL), frequently referred to informally as a web address. More rarely seen in usage is the Uniform Resource Name (URN), which was designed to complement URLs by providing a mechanism for the identification of resources in particular namespaces.

Unique Ingredient Identifier

The Unique Ingredient Identifier (UNII) is a non-proprietary, free, unique, unambiguous, non-semantic, alphanumeric identifier linked to a substance's molecular structure or descriptive information by the Substance Registration System (SRS) of the Food and Drug Administration (FDA) and the United States Pharmacopeia (USP).

The SRS is used to generate permanent, unique identifiers for substances in regulated products, such as ingredients in drug and biologic products. The SRS uses molecular structure and descriptive information to define a substance and generate the UNII. The primary means for defining a substance is by its molecular structure as represented on a two-dimensional plane. When a molecular structure is not available (e.g., botanicals), the UNII is defined by descriptive information.The procedures and management of the SRS is provided by the SRS Board which includes experts from both FDA and the United States Pharmacopoeia (USP).

Universally unique identifier

A universally unique identifier (UUID) is a 128-bit number used to identify information in computer systems. The term globally unique identifier (GUID) is also used, typically in software created by Microsoft.

When generated according to the standard methods, UUIDs are for practical purposes unique, without depending for their uniqueness on a central registration authority or coordination between the parties generating them, unlike most other numbering schemes. While the probability that a UUID will be duplicated is not zero, it is close enough to zero to be negligible.

Thus, anyone can create a UUID and use it to identify something with near certainty that the identifier does not duplicate one that has already been, or will be, created to identify something else. Information labeled with UUIDs by independent parties can therefore be later combined into a single database or transmitted on the same channel, with a negligible probability of duplication.

Adoption of UUIDs and GUIDs is widespread, with many computing platforms providing support for generating them and for parsing their textual representation.

Personal name
By sequence
By trait
By life situation
Pseudonyms (list)
By culture
Surnames by country
Courtesy names
Religious names
Manners of address
Related traditions

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