ISO 34000:2023

INTERNATIONAL ISO
STANDARD 34000
First edition
2023-10
Date and time — Vocabulary
Date et l'heure — Vocabulaire
Reference number
© ISO 2023
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms related to general concepts .1
4 Terms related to time scales . 4
5 Terms related to clock systems . .7
6 Terms related to calendar systems . 8
7 Terms related to time scale units .10
8 Terms related to expressions and representations .15
Bibliography .18
Index .19
iii
Foreword
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iv
Introduction
ISO documents relating to date and time concepts have been available since 1971.
This document presents terms and definitions for selected concepts relevant to date and time concepts
and of their representation.
Specifically, the terminology presented in this document:
— serves as a sound basis in the understanding of date and time;
— guides new developments in the field by underpinning mutual understanding;
— serves as a quick and handy reference for those newly inaugurated to this field.
In this document, the decimal sign is a comma on the line, and each group of three digits are separated
by a small space from the preceding digits, counting from the decimal sign, in accordance with the ISO/
IEC Directives, Part 2.
However, Resolution 10 of the 22nd General Conference on Weights and Measures (Conférence Générale
des Poids et Mesures, CGPM) in 2003 stated that:
“The decimal marker shall be either a point on the line or a comma on the line.”
And reaffirmed the following resolution from Resolution 7 of the 9th CGPM, 1948:
“Numbers may be divided in groups of three in order to facilitate reading.”
In practice, the choice between these alternatives depends on customary use in the language concerned.
In the technical areas of date and time, it is customary for the decimal point always to be used, and that
numbers are not grouped, for all languages.
v
INTERNATIONAL STANDARD ISO 34000:2023(E)
Date and time — Vocabulary
1 Scope
This document defines terms related to date and time, from fundamental concepts to those of their
usage and representation.
2 Normative references
There are no normative references in this document.
3 Terms related to general concepts
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
date
time (3.2) on the calendar system (6.1) time scale (3.5)
Note 1 to entry: Common forms of date include calendar date (7.8), ordinal date (7.9) and week date (7.10).
3.2
time
mark attributed to an instant (3.4) or a time interval (3.6) on a specified time scale (3.5)
Note 1 to entry: The term “time” is often used in common language. However, it should only be used if the meaning
is clearly visible from the context.
Note 2 to entry: On a time scale consisting of successive time intervals, such as a clock system (5.1) or calendar
system (6.1), distinct instants may be expressed by the same time.
Note 3 to entry: This definition corresponds with the definition of the term “date” in IEC 60050-113:2011, 113-
01-12.
3.2.1
proper time
time (3.2) on a proper time scale (4.1)
[9]
Note 1 to entry: See ITU-R TF.2018-0 and the BIPM SI Brochure for additional information.
3.2.2
coordinate time
time on a coordinate time scale (4.2)
Note 1 to entry: Coordinate time is a mathematical coordinate in the four-dimensional space-time of the
coordinate system. For a given event, the coordinate time has the same value everywhere.
Note 2 to entry: Coordinate times are not measured; rather, they are computed from the proper times (3.2.1) of
clocks.
Note 3 to entry: The relation between coordinate time and proper time depends on the clock’s position and state
of motion in its gravitational environment and is derived by integration of the space-time interval.
[9]
Note 4 to entry: See ITU-R TF.2018-0 and BIPM SI Brochure for additional information.
3.3
time axis
mathematical representation of the succession in time according to the space-time reference of
instantaneous events along a unique axis
Note 1 to entry: According to the theory of special relativity, the time axis depends on the choice of a spatial
reference frame.
Note 2 to entry: In IEC 60050-113:2011, 113-01-03, time according to the space-time reference is defined to be
the one-dimensional subspace of space-time, locally orthogonal to space.
[SOURCE: IEC 60050-113:2011, 113-01-07, modified — In the definition, “time” is clarified as “time
according to the space-time reference”; in note 1 to entry, the phrase “special theory of relativity” has
been changed to “theory of special relativity” for clarity; note 2 to entry has been added.]
3.4
instant
point on the time axis (3.3)
Note 1 to entry: An instantaneous event occurs at a specific instant.
[SOURCE: IEC 60050-113:2011, 113-01-08]
3.5
time scale
timescale
system of ordered marks which can be attributed to instants (3.4) on the time axis (3.3), one instant
being chosen as the origin
EXAMPLE 1 TAI (4.9) is a continuous time scale.
EXAMPLE 2 UTC (4.7) is a time scale that is continuous but contains discontinuities. Discontinuities in UTC
arise from the mechanism of inserting leap seconds (4.8).
EXAMPLE 3 Local time (4.6) with periodic changing of offsets from UTC during the year, such as seasonal time
changes like summer time and winter time, results in a time scale that is continuous with discontinuities.
EXAMPLE 4 A calendar system (6.1) is a time scale composed of successive steps, with the time axis split up
into a succession of consecutive time intervals (3.6), where the same mark is attributed to all instants of each
time interval. For instance, all instants within a calendar day (7.13) are referred to by a reference to that calendar
day only.
EXAMPLE 5 In signal processing, the process of sampling results in a discrete time scale.
Note 1 to entry: The system of ordered marks may be of the following nature: continuous, continuous with
discontinuities, in successive steps, or discrete.
Note 2 to entry: The definition, notes to entry and EXAMPLEs are derived from IEC 60050-113:2011, 113-01-11,
“timescale”.
3.6
time interval
part of the time axis (3.3) limited by two instants (3.4)
Note 1 to entry: Unless otherwise stated, a time interval is by default a closed time interval (3.6.1), which includes
the limiting instants themselves.
[SOURCE: IEC 60050-113:2011, 113-01-10, modified – The original NOTEs have been deleted; note 1 to
entry has been added.]
3.6.1
closed time interval
[a,b]
time interval (3.6) that includes both the beginning instant (3.4) and the final instant
3.6.2
open time interval
(a,b)
time interval (3.6) that does not include either the beginning instant (3.4) or the final instant
3.6.3
right half-open time interval
contiguous time interval
[a,b)
time interval (3.6) that includes the beginning instant (3.4) but not the final instant
3.6.4
left half-open time interval
(a,b]
time interval (3.6) that includes the final instant (3.4) but not the beginning instant
3.6.5
recurring time interval
series of consecutive time intervals (3.6) of identical duration (3.7)
Note 1 to entry: If the duration of the time intervals is measured in calendar system (6.1) entities, the duration of
each time interval depends on the calendar dates (7.8) of its start and its end.
Note 2 to entry: If the starting instants (3.4) of time intervals are repeated according to a set of rules, the “repeat
rules for recurring time intervals” in ISO 8601-2:2019, Clause 5 apply.
3.7
duration
non-negative quantity attributed to a time interval (3.6), the value of which is equal to the difference
between the quantitative times of the final instant (3.4) and the initial instant of the time interval
Note 1 to entry: Duration is one of the base quantities in the International System of Quantities (ISQ) on which SI
is based. The term “time” instead of “duration” is often used in this context and also for an infinitesimal duration.
Note 2 to entry: For the term “duration”, expressions such as “time” or “time interval” are often used, but the
term “time” is not recommended in this sense and the term “time interval” is deprecated in this sense to avoid
confusion with the concept of “time interval”.
Note 3 to entry: The exact duration of a time scale unit (7.1) depends on the time scale (3.5) used. For example,
the durations of a year, month, week, day, hour, or minute, may depend on when they occur (e.g. in a Gregorian
calendar, a calendar month (7.21) can have a duration of 28, 29, 30, or 31 days; in a 24-hour clock system (5.2), a
clock minute (7.5) can have a duration of 59, 60, or 61 seconds). Therefore, the exact duration of a time scale unit
can only be evaluated if the exact duration of each composing element is known.
Note 4 to entry: The SI unit of duration is second (7.2). Time scale units derived from the SI second (7.2)
...