NOMINAL NUMBERS or CATEGORICAL NUMBERS are numeric codes, meaning numerals used for labelling or identification only. The values of the numerals are irrelevant, and they do not indicate quantity, rank, or any other measurement.
* 1 Definition
* 1.1 Use of nominal numbers
* 2 Examples
* 2.1 Narrowly defined
* 3 See also * 4 External links
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 "...merely statements of qualitative category of membership." This usage comes from the sense of nominal as "name".
Mathematically, nominal numbering is a one-to-one and onto function from a set of objects being named to a set of numerals, which may change (typically growing) over time: it is a function because each object is assigned a single numeral, it is one-to-one because different objects are assigned different numerals, and it is onto because every numeral in the set at a given time has associated with it a single named object.
"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,
In general, the only meaningful operation with nominal numbers is to compare two nominal numbers to see whether they are identical or not (whether they refer to the same object). Numbers 102 and 400: bus route 102 in London , run by an Alexander Dennis Enviro400 double-decker bus . Number 107: the car Peugeot 107 .
A great variety of numbers meet the broad definition, including:
* National identification numbers , such as:
* Social Security numbers * Driver\'s license numbers * National Insurance number
* Bank codes and sort codes , like IBAN , and the ABA Routing transit number . * Postal codes , such as ZIP codes (These are generally numeric in the United States, but other nations often use alphanumeric systems.) * Telephone numbers , assigned by various telephone numbering plans , such as the ITU-T E.164 and the North American Numbering Plan (NANPA). * Numbers of train or bus routes in public transport
These are usually assigned either in some hierarchical way, such as
how telephone numbers are assigned (in NANPA) as
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