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An identifier (also a label ) is a feature linked to a specific identity for the unique identification of the supporting object.

For example, a house number identifies a specific house as an identifier within a street. In databases , identifiers as identifiers of a data record are also referred to as database identifiers or master numbers . Here identifiers are usually as components of numbers or codes of alphanumeric characters used, among other things, number code (numbers or numeric code and alphanumeric codes) or letter codes is spoken. Linguistic identifiers (for example identifiers in a computer program or descriptors in a controlled vocabulary ) and other features, for example color coding (such as the colors red and green for port and starboard ) are also possible. In addition, biometric features can be qualified as identifiers.


In principle, identifiers can be used to identify any object, from products ( serial numbers , catalog numbers) to people ( ID numbers) and abstract ideas ( notation of a topic).

The identification ("ID" for short) of products and their components in the context of the documentation of technical products is a comprehensive field of application .

A clear identification of all production and procurement objects is of central importance for the various business functions of a company.

In the commercial sector, there are four types of identifier encryption:

  • the purely identifying encryption
  • partially identifying, partially classifying encryption (compound key)
  • the characteristic-related (classifying) encryption
  • the logical or set-algebraic encryption

Numbers and letters are usually used for the key. In the case of classifying keys, the letters or numbers have a specific meaning; they say something about the object or its properties.

Structure and management of identifiers

The entirety of all identifiers of a region forms a controlled vocabulary . For example, all of mathematics is subdivided into sub-areas using the Mathematics Subject Classification , each of which is assigned a notation .

The identification number is often seen as an abbreviation . In terms of coding theory, however, this is not always the case: The ID number should separate different objects from one another as concisely as possible. Since it is usually embedded in an identification system, it is often only based on an easily remembered term.

Example: A for motorway , B for federal road , L for state road , but the actual terms refer to an assignment of responsibility that has shifted to other institutions in the course of reforms.

In the IT area, of course, the evaluation of computers is often carried out and therefore no redundancy would be necessary here, but it is often built in for error correction.

Identification system

A system of identifiers must always be designed in such a way that an unambiguous assignment between the identifier and what is designated is possible. The uniqueness in the reverse direction is also desirable. Expressed mathematically, the assignment of the set of identifiers to the set of those to be identified is then one-to-one ( bijective ).

A number code is kept in such a way that it assigns exactly one number to a single date, data record or object, which clearly identifies it:

  • An example of an identification number is the telephone number as an assignment to the corresponding subscriber (connection) with whom one would like to call. In relation to a specific person, however, it is not unique if, for example, several people live in one household. So you have to clarify who you want to talk to. The development of extensions as well as that of cell phones is partly motivated by precisely this deficiency (personal reference instead of location reference of the identifier due to changed communication behavior).
  • Another example is the International Standard Book Number (ISBN), by means of which a book is clearly specified in a short way. An additional check digit is added to the identification number for error correction .
  • In a computer network , IP addresses are found as identification numbers for servers . For us humans, domains are also created as identifiers.

Automatic identification

If computer systems are to recognize objects or people, certain identifiers are used. The corresponding processes are classified according to different methods. The identifier must have a physical carrier and be recognizable from the object to be identified. The physical form should be able to be read reliably and quickly. Well-known examples are barcodes , RFID and magnetic stripe cards . An exception to direct identification is biometrics .


Identifiers, specifically to durability ( persistency are created), are also known as persistent identifiers (persistent identifier) designated. (See also permalink ).

Use in databases

Identifiers in databases can be given both by an attribute or a column of a database table and by a selection of several attributes. In the case of identification by several attributes, the totality of the selected attributes forms the identification. So is z. As in a database table employees a person by the three attributes name , first name , birthday identifiable.


See also


  • Bruno Grupp: Optimal encryption for online data processing. Development of modern numbering systems for part numbers of all kinds, personal numbers and order numbers . Verlag TÜV Rheinland, Cologne 1987, ISBN 3-88585-344-2 .

Individual evidence

  1. Wilmjakob Herlyn: PPS in the automotive industry. Production program planning and control of vehicles and assemblies . Hanser, Munich 2012, ISBN 978-3-446-41370-2 , pp. 80 ff .