Nominal number

Nominal number

Nominal numbers (sometimes called categorical numbers) are numerals used for identification only. The numerical value is irrelevant, and they do not indicate quantity, rank, or any other measurement.



The term "nominal number" is quite recent and of limited use. It appears to have originated as a usage in school textbooks derived from the statistical term "nominal data", defined as data indicating "...[m]erely statements of qualitative category of membership." This usage comes from the sense of nominal as "name".

Mathematically, nominal numbering is a one-to-one function from a set of objects being named to the set of numerals: it is a function because each object is assigned a numeral, and it is one-to-one because different objects are assigned different numerals.

"Nominal number" can be broadly defined as "any numeral used for identification, however it was assigned", or narrowly as "a numeral with no information other than identification".

For the purposes of naming, the term "number" is often used loosely to refer to any string (sequence of symbols), which may not consist entirely of digits—it is often alphanumeric. For instance, National Insurance numbers, some driver's license numbers, and some serial numbers contain letters.

Use of nominal numbers

"Nominal" refers to the use of numbers: any nominal number can be used by its numerical value as an integer—added to another, multiplied, compared in magnitude, and so forth—but for nominal numbers these operations are not in general meaningful. For example, the ZIP code 11111 is less than the ZIP code 12345, but that does not mean that 11111 was issued before 12345 or that the region denoted by 11111 is further south than 12345, though it might be. Similarly, one can add or subtract ZIP codes, but this is meaningless: 11111 - 12345 does not have any meaning as a ZIP code.

In general, the only meaningful operation with nominal numbers is to compare two nominal numbers to see whether they are equal or not (whether they refer to the same object).


A great variety of numbers meet the broad definition, including:

These are usually assigned either in some hierarchical way, such as how telephone numbers are assigned (in NANPA) as Country Code + Area Code + Prefix + Suffix, where the first 3 are geographically based, or sequentially, as in serial numbers; these latter are thus properly ordinal numbers.

Narrowly defined

Numerical identifiers that are nominal numbers narrowly defined, viz, convey no information other than identity, are quite rare. These must be defined either arbitrarily or randomly, and most commonly arise in computer applications, such as dynamic IP addresses assigned by Dynamic Host Configuration Protocol. A more everyday example are sports squad numbers, which do not in general have any public meaning beyond identity, though they may be allocated based on some internal club or organization policy. In some settings these are based on position, but in others they are associated with an individual, being a proper nominal number. The naming function is demonstrated by retired numbers, where a club "retires" a number that has become associated with a particularly famous player, but reallocate others to new players when they become available.

See also


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Nominal (disambiguation) — A nominal is one of the parts of speech. Nominal may also refer to: Nominal aphasia, a problem remembering words and names Nominal category, a group of objects or ideas that can be collectively grouped on the basis of shared, arbitrary… …   Wikipedia

  • Nominal impedance — in electrical engineering and audio engineering refers to the approximate designed impedance of an electrical circuit or device. The term is applied in a number of different fields, most often being encountered in respect of: The nominal value of …   Wikipedia

  • Nominal Pipe Size — (NPS) is a North American set of standard sizes for pipes used for high or low pressures and temperatures.[1] Pipe size is specified with two non dimensional numbers: a nominal pipe size (NPS) for diameter based on inches, and a schedule (Sched.… …   Wikipedia

  • Nominal Accounting — Nominal Small Business Accounting software is a new software product released to Australian Market. It is one of a number of products[1] to support the new government Standard Business Reporting initiative. Nominal Accounting has the following… …   Wikipedia

  • Nominal group technique — The nominal group technique (NGT) is a decision making method for use among groups of many sizes, who want to make their decision quickly, as by a vote, but want everyone s opinions taken into account (as opposed to traditional voting, where only …   Wikipedia

  • Nominal size — In manufacturing, a nominal size or trade size is a size in name only used for identification.[1] The nominal size may not match any dimension of the product, but within the domain of that product the nominal size may correspond to a large number …   Wikipedia

  • Nominal interest rate — In finance and economics nominal interest rate or nominal rate of interest refers to the rate of interest before adjustment for inflation (in contrast with the real interest rate); or, for interest rates as stated without adjustment for the full… …   Wikipedia

  • Nominal group (functional grammar) — Those five beautiful shiny Jonathan apples sitting on the chair In systemic functional grammar (SFG), a nominal group is a group of words which expresses an entity. A nominal group is widely regarded as synonymous to noun phrase in other… …   Wikipedia

  • Nominal income target — A nominal income target is a potential policy conducted by a central bank to target the future level[1] of economic activity in nominal terms (ie. not adjusted for inflation). The central bank could target Gross domestic product (NGDP) or Gross… …   Wikipedia

  • Nominal group (language) — In English, a nominal group typically comprises a noun surrounded by other items (words) that all in some way characterise that noun. Within a clause, a nominal group functions as though it is that noun, which is referred to as the head ; the… …   Wikipedia