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] substance (or class thereof).

Description

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.

Arbitary IDs

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 he is speaking casually and imprecisely.

Metadata

ID codes 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.

No metadata

Arbitrary identifiers carry no metadata.

For example, if your food package just says 100054678214, its ID may not tell you anything except identity—no date, manufacturer name, production sequence rank, or inspector number.

Information leak problems

In some cases, even arbitrary identifiers such as sequential serial numbers leak too much information (see German tank problem). Opaque identifiers—identifiers designed to avoid leaking even that small amount of information—include "really opaque pointers" and Version 4 UUIDs.

Unique identifier

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.

Denotation and connotation

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.

See also

• Barcode
• Binomial nomenclature
• British Approved Name
• Chemical nomenclature
• Computer science
• Data
• Data (computing)
• Data descriptor
• Data element
• Descriptor
• Diagnosis code
• Document management system
• Enumerated type
• File descriptor
• Food labeling regulations
• Gene nomenclature
• German tank problem
• Handle (computing)
• Identification
• Identity (object-oriented programming)
• Identity document
• Index term
• International Code of Nomenclature for algae, fungi, and plants
• International Code of Nomenclature of Bacteria
• International Code of Nomenclature for Cultivated Plants
• International Code of Zoological Nomenclature
• Marketing part number
• Metadata
• Name binding
• Namespace
• Naming convention (programming)
• National identification number
• Nomenclature – contains various standardized naming systems
• Nomenclature code
• Object (computer science)
• Overloading
• Part number
• Product code
• Reference (computer science)
• Representation term
• Systematized Nomenclature of Medicine
• Uniform resource identifier (URI)
• Unique identifier
• Unique key

External links

• Identifier @ Wikipedia