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 noncountable substance (or class thereof). The abbreviation ID (or 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.
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, 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, 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.
A resource may carry multiple identifiers. Typical examples are:
The inverse is also possible, where multiple resources are represented with the same identifier (discussed below).
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 had not, 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.
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 (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 |
In computing, a namespace is a set of signs (names) that are used to identify and refer to objects of various kinds. A namespace ensures that all of a given set of objects have unique names so that they can be easily identified.
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 also fit within the URI system. They are widely used to identify academic, professional, and government information, such as journal articles, research reports, data sets, and official publications.
In computing, the process identifier is a number used by most operating system kernels—such as those of Unix, macOS and Windows—to uniquely identify an active process. This number may be used as a parameter in various function calls, allowing processes to be manipulated, such as adjusting the process's priority or killing it altogether.
The Electronic Product Code (EPC) is designed as a universal identifier that provides a unique identity for every physical object anywhere in the world, for all time. The EPC structure is defined in the EPCglobal Tag Data Standard, which is a freely available standard. The canonical representation of an EPC is a URI, namely the 'pure-identity URI' representation that is intended for use when referring to a specific physical object in communications about EPCs among information systems and business application software.
In compiler construction, name mangling is a technique used to solve various problems caused by the need to resolve unique names for programming entities in many modern programming languages.
In Unix-like systems, multiple users can be put into groups. POSIX and conventional Unix file system permissions are organized into three classes, user, group, and others. The use of groups allows additional abilities to be delegated in an organized fashion, such as access to disks, printers, and other peripherals. This method, among others, also enables the superuser to delegate some administrative tasks to normal users, similar to the Administrators group on Microsoft Windows NT and its derivatives.
Unix-like operating systems identify a user by a value called a user identifier, often abbreviated to user ID or UID. The UID, along with the group identifier (GID) and other access control criteria, is used to determine which system resources a user can access. The password file maps textual user names to UIDs. UIDs are stored in the inodes of the Unix file system, running processes, tar archives, and the now-obsolete Network Information Service. In POSIX-compliant environments, the shell command id
gives the current user's UID, as well as more information such as the user name, primary user group and group identifier (GID).
UID may refer to:
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 and information systems. In general, it was associated with an atomic data type.
Catalogue Service for the Web (CSW), sometimes seen as Catalogue Service - Web, is a standard for exposing a catalogue of geospatial records in XML on the Internet. The catalogue is made up of records that describe geospatial data, geospatial services, and related resources.
Object Manager is a subsystem implemented as part of the Windows Executive which manages Windows resources. Resources, which are surfaced as logical objects, each reside in a namespace for categorization. Resources can be physical devices, files or folders on volumes, Registry entries or even running processes. All objects representing resources have an Object Type
property and other metadata about the resource. Object Manager is a shared resource, and all subsystems that deal with the resources have to pass through the Object Manager.
A file format is a standard way that information is encoded for storage in a computer file. It specifies how bits are used to encode information in a digital storage medium. File formats may be either proprietary or free.
MIL-STD-130, "Identification Marking of U.S. Military Property," is a specification that describes markings required on items sold to the Department of Defense (DoD), including the addition, in about 2005, of UII Data Matrix machine-readable information (MRI) requirements. MIL-STD-130 describes the materials allowed, minimum text size and fonts, format, syntax and rules for identifying marks on a part, where to locate this marking plus exceptions and unique situations, such as vehicle identification numbers, cell phone IDs, etc. Other non-identifying markings—such as "this end up"—are covered under MIL-STD-129.
Unique Identification Marking, UID marking, Item Unique Identification or IUID, is a part of the compliance process mandated by the United States Department of Defense. It is a permanent marking method used to give equipment a unique ID. Marking is essential for all equipment with an acquisition cost of over $5,000, equipment which is mission essential, controlled inventory, or serially-controlled. UID-marking is a set of data for assets that is globally unique and unambiguous. The technology used to mark an item is 2D Data Matrix ECC 200 Symbol. UID marking can be used to ensure data integrity and data quality throughout an item's lifecycle; it also supports multi-faceted business applications.
Identity correlation is, in information systems, a process that reconciles and validates the proper ownership of disparate user account login IDs that reside on systems and applications throughout an organization and can permanently link ownership of those user account login IDs to particular individuals by assigning a unique identifier to all validated account login IDs.
The Handle System is the Corporation for National Research Initiatives's proprietary registry assigning persistent identifiers, or handles, to information resources, and for resolving "those handles into the information necessary to locate, access, and otherwise make use of the resources".
An Extensible Resource Identifier (XRI) is a scheme and resolution protocol for abstract identifiers compatible with Uniform Resource Identifiers (URI) and Internationalized Resource Identifiers (IRI), developed by the XRI Technical Committee at OASIS. The goal of XRI was a standard syntax and discovery format for abstract, structured identifiers that are domain-, location-, application-, and transport-independent, so they can be shared across any number of domains, directories, and interaction protocols.
The Entertainment Identifier Registry, or EIDR, is a global unique identifier system for a broad array of audiovisual objects, including motion pictures, television, and radio programs. The identification system resolves an identifier to a metadata record that is associated with top-level titles, edits, DVDs, encodings, clips, and mashups. EIDR also provides identifiers for video service providers, such as broadcast and cable networks.
Lex is a URN namespace, a type of Uniform Resource Name (URN), that allows accurate identification of laws and other legal norms.
Namespaces are a feature of the Linux kernel that partition kernel resources such that one set of processes sees one set of resources, while another set of processes sees a different set of resources. The feature works by having the same namespace for a set of resources and processes, but those namespaces refer to distinct resources. Resources may exist in multiple namespaces. Examples of such resources are process IDs, host-names, user IDs, file names, some names associated with network access, and Inter-process communication.