Unique identifier

Not to be confused with Unique Identification Number (which also is referred to by the abbreviation UID).

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
• 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.

Examples

• Electronic Product Code (EPC)
• Part number
• Universally Unique Identifier
• Numbering scheme
• Track & Trace

Chemistry

• IUPAC nomenclature
• CAS registry number

Computing

• Organizationally Unique Identifier
• Globally Unique Identifier
• Universally Unique Identifier
• Identity correlation
• World Wide Port Name
• MAC address

Economics

• Harmonized System

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)

Legal

• Bates numbering

Mathematical publications

• Mathematical Reviews number
• Zentralblatt MATH identifier

Science

• Systematic name

Transportation

• Airport codes
• Maritime Mobile Service Identity
• ISO 6346 for shipping containers
• UIC wagon numbers
• Reporting marks