With reference to a given (possibly implicit) set of objects, a unique identifier (UID) is any identifier which is guaranteed to be unique among all identifiers used for those objects and for a specific purpose. There are three main types of unique identifiers, each corresponding to a different generation strategy:
- serial numbers, assigned incrementally or sequentially
- random numbers, selected from a number space much larger than the maximum (or expected) number of objects to be identified. 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 such as the EPC Information Services.
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.
- National identification number
- ORCID (Open Researcher and Contributor ID)
- Digital object identifiers
- Electronic Product Code (EPC)
- Stock Keeping Unit (SKU)
- Part number
- Universally Unique Identifier
- Numbering scheme
- Track & Trace
- Bank card number
National identification number
National identification number is used by the governments of many countries as a means of tracking their citizens, permanent residents, and temporary residents for the purposes of work, taxation, government benefits, health care, and other governance-related functions.
- Organizationally Unique Identifier
- Globally Unique Identifier
- Universally Unique Identifier
- Identity correlation
- World Wide Port Name
- MAC address
Economics, tax and regulation
Internet architecture and standards
- Request for Comments (RFC)
- Internet Standard (STD)
- Best Current Practice (BCP)
- For Your Information (FYI)
- Internet Draft (I-D)
- Internet Experiment Note (IEN)
- RARE Technical Reports (RTR)
- International Air Transport Association airport codes
- Maritime Mobile Service Identity
- IMO number to identify sea-going ships
- IMO container codes according to ISO 6346 for shipping containers
- UIC wagon numbers
- American rail transportation Reporting marks
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