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.
1.1 Use of nominal numbers
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, the ZIP code
11111 is less than the
Numbers 102 and 400: bus route 102 in London, run by an Alexander Dennis Enviro400 double-decker bus.
Number 107: the car
Examples A great variety of numbers meet the broad definition, including:
National identification numbers, such as:
Social Security numbers
Bank codes and sort codes, such as International Bank Account Numbers
or ABA routing transit numbers.
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
E.164 and the
North American Numbering Plan
These are usually assigned either in some hierarchical way, such as
how telephone numbers are assigned (in NANPA) as
Serial number Symbol (programming) Unique key Universally Unique Identifier
Cardinal, Ordinal and Nominal Numbers Cardinal, Ordinal, and Nominal Numbers Posamentier, Alfred S.; Farber, William; Germain-Williams, Terri L.; Paris, Elaine; Thaller, Bernd; Lehmann, Ingmar (2013). "Nominal Numbers". 100 Commonly Asked Questions in Math Class. p. 60. ISBN 978-1-4833-3