With reference to a given (possibly implicit) set of objects, a unique identifier is any identifier which is guaranteed to be unique among all identifiers used for those objects and for a specific purpose. In Computer science, Identifiers ( IDs) are lexical tokens that name entities. There are three main types of unique identifiers, each corresponding to a different generation strategy:

• serial numbers, assigned incrementally
• random numbers, selected from a number space much larger than the maximum (or expected) number of objects to be identified. A serial number is a unique Number assigned for Identification which varies from its Successor or Predecessor by a fixed discrete Integer A random number generator (often abbreviated as RNG is a computational or physical device designed to generate a sequence of Numbers or symbols that lack any Although not really unique, some identifiers of this type may be appropriate for identifying objects in many practical applications and are, with abuse of language, still referred to as "unique"
• names or codes allocated by choice which are forced to be unique by keeping a central registry

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.

In relational databases, certain attributes of an entity that serve as unique identifiers are called primary keys. A relational database is a Database that groups data using common attributes found in the data set An entity-relationship model (ERM is an abstract conceptual representation of structured data In Relational database design a unique key or primary key is a Candidate key to uniquely identify each row in a table.

Contents 1 See also 1.1 Computing 1.2 Economics 1.3 Legal 1.4 Science 1.5 Chemistry

See also

• Identifier
• Universally Unique Identifier
• Numbering scheme

Computing

• Organizationally Unique Identifier
• WWPN
• MAC address

Economics

• Harmonized System

Legal

• Bates numbering

Science

• Systematic name

Chemistry

• IUPAC nomenclature
• CAS registry number

In Computer science, Identifiers ( IDs) are lexical tokens that name entities. A Universally Unique Identifier (UUID is an identifier standard used in Software construction standardized by the Open Software Foundation (OSF as part of the There are many different numbering schemes for assigning Nominal numbers to entities An Organizationally Unique Identifier ( OUI) is a 24-bit number that is purchased from the Institute of Electrical and Electronics Engineers Incorporated (IEEE In Computer networking a Media Access Control address ( MAC address) or Ethernet Hardware Address ( EHA) hardware address The Harmonised Commodity Description and Coding System (HS of tariff nomenclature is an internationally standardized system of names and numbers for classifying traded products developed Bates numbering (also known as Bates stamping or Bates coding) is used in the legal medical and business fields to place identifying numbers and/or date/time-marks There are millions of possible objects that can be described in science too many to create Common names for every one IUPAC Nomenclature is a system of naming Chemical compounds and of describing the science of Chemistry in general CAS registry numbers are unique numerical identifiers for Chemical compounds Polymers biological sequences mixtures and Alloys They are also referred to

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