INTERNATIONAL STANDARD FOR DENOTATION OF CALENDAR TIME

 

INTRODUCTION

The lack of a unified way of representing calendar time leads to unnecessary confusion and mistakes in vital communications regarding events in time. There exists an internationally adopted standard which provides a working solution to this problem - the ISO standard 8601.
This text is a short presentation of ISO 8601 with annotations added by the author.

 

ISO 8601 - RECOMMENDATIONS AND STANDARDS

ISO 8601 is the denotation of the International Standard "Data elements and interchange formats - Information interchange - Representation of dates and times".
The International Organization for Standardization (ISO) says:
"The promotion of this International Standard will not only facilitate interchange across international boundaries, but will also improve the portability of software, and will ease problems of communication within an organization, as well as between organizations".
The International Standard does not cover denotation of calendar time where words are used in the representation.
ISO has recommended a standard for denoting a date by figures in the sequence year, month and day since 1970.
Despite the existence of this standard, different forms of numeric denotation of date have been commonly used in different countries. The ISO 8601 standard has been applicable since 1988. This standard includes specifications for the numeric denotation of day but also numeric denotations of point of time and space of time.
The European Committee for Standardization (CEN) has also accepted ISO 8601 as the standard (EN 28601) for its national members Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.

 

CALENDAR TIME - THE GREGORIAN CALENDAR

Calendar time means running time according to a given time base, e.g. the Gregorian calendar.
The Gregorian calendar may be regarded as a "world standard" for the continuous reckoning of time. Even among nations that apply other systems of time reckoning are arrival- and departure times in communication timetables expressed according to the Gregorian system of reckoning. However, the number of work-free days (holidays) and when they take place, deviate even among different countries that adopt the Gregorian calendar. This calendar was first introduced in the year 1582 and adopted in Britain in the year 1752.

Apart from the Gregorian calendar there are about 40 other calendars in use throughout the world.
There is no year zero in the Gregorian calendar. Only one year had elapsed at the beginning of the year denoted 2 AD (Anno Domini) since the Epoch of the Christian Era. A period of only 1999 - not 2000 - years will have elapsed at midnight on 31 December 1999. It is therefore clear that the New Millennium will begin at zero o´clock on 1st January 2001.
The International Standard ISO 8601 is based upon the Gregorian calendar.

DENOTATION OF A PARTICULAR DAY (24 HOURS) OR DATE - THE GUIDING RULES

The guiding rules:
The calendar date shall be denoted by eight numeric characters; in the sequence
year [CCYY], month [MM] and day [DD].
The allowed values for calendar year are [0001] through [9999].
When desired, the character hyphen [-] can be used to separate "year" and "month", and "month" and "day".
Example: The 2nd May 2001 is written 20010502 or 2001-05-02 .

Annotation 1:
Although it is acceptable in ISO 8601 to write 2nd May 2001 as 010502 or 01-05-02 it could lead to serious misunderstandings, especially during the years 2001/2031.
Example: A date written as 010502 - which date is that? Is it 1st May 2002 (Britain) or is it 5th January 2002 (USA) or is it 2nd May 2001 (ISO)?
The objectionable habit to express the year with only two instead of four digits is the main cause to the "Year 2000 problem (Y2K-bug)".
To exclude the two digits representing the century is therefore very unwise.

Annotation 2:
The American National Standard Institute (ANSI) standard is limited to the
representation of calendar date for interchange among data systems only and it is not designed for (nor does it preclude) usage by humans as input to or output from data systems.
No separators are allowed between year, month and day, but the denotation by figures is the same as in the International Standard.
The standard document is ANSI X3.30-1998.
Example: The fourth day of July in the year 1776 is denoted as "17760704".

DENOTATION OF POINT OF TIME - THE GUIDING RULES

Point of time means a co-ordinate (point) on a time scale (at a specific place).

The guiding rules:
A point of time in the Gregorian calendar can be identified by means of a unique expression giving a specific date and a specific stroke of clock within that date.
The order year, month, day can be extended by hour, minute, second and decimal fraction of a second, in order to denote points of time numerically.
The ISO standard is based on the 24-hour timekeeping system.

A point of time shall be denoted in the sequence year [CCYY], month [MM], day [DD], hour [hh], minute [mm] and second [ss,s]. Leading zeroes in each time component are required.
The letter T shall be used as time designator to indicate the combination of date and stroke of the clock. By mutual agreement of the partners in information interchange, the character [T] may be omitted.
When desired, the character colon [:] can be used to separate "hour" and "minute", and "minute" and "second".
Example: The 2nd May 2001, 11.15 pm or 23.15 hours may be written as 20010502T2315 or 2001-05-02T23:15.

If a point of time is converted into Coordinated Universal Time (UTC) the time zone designator [Z] shall be added to the notation. UTC is commonly known as GMT. Example: 2001-05-02T22:15Z.

The differences between local time and UTC shall be expressed as positive if the local time is ahead of UTC and as negative if it is behind.
Example: 2001-05-02 T23:15 +01:00 (local time).

Annotation 3:
The ANSI standard is limited to the representation of time for interchange among data systems only and it is not designed for (nor does it preclude) usage by humans as input to or output from data systems.
No separators are allowed between date and stroke of clock or between hour and minute, and minute and second, but the denotation by figures is the same as in the International Standard. When a decimal fraction of a second is specified it shall be separated from the second by a decimal point (ISO prefers comma as the decimal sign).
The standard document is ANSI NCITS 310-1998.
Example: 39 minutes and 25.6 seconds past 7 o´clock in the afternoon of the fourth day of July in the year 1776 is denoted as "17760704193925.6".

DENOTATION OF SPACE OF TIME - THE GUIDING RULES

Space of time means the time between two points of time on the same time scale.

The guiding rules:
A space of time can be specified by denoting those two points of time that indicate the beginning and the end of the time period concerned. The character solidus [/] shall be used to separate the two points of time, intended to indicate a specific space of time.
Examples:
2001-05-02T23:15/2002-02-03T13:00
2001-05-02T08:15/10:30 (within the same day)
2001-05-02/31 (i.e. 2001-05-02T00:00/2001-05-31T24:00)
2001-05/10 (i.e. 2001-05-01T00:00/2001-10-31T24:00)
2001/2002 (i.e. 2001-01-01T00:00/2002-12-31T24:00)

Annotation 4:
If the actual stroke of the clock is not indicated, the period of time is reckoned to begin at 00:00 o'clock on the first day and end at 24:00 o'clock on the last day of the period concerned.

Annotation 5:
ANSI does not have a standard for the above.

NUMBERING OF "COMMERCIAL" WEEKS - THE GUIDING RULES

The guiding rules:
A week number should always stand for a space of time of seven days. For the purpose of week numbering, the first day of a week should be Monday. (The first day of the "traditional" week is Sunday and has been for several thousand years).
Week number one is the first week containing four days or more of the new year. (Week number 53 takes place with an interval of five to six years).
The letter W shall be used as a week designator preceding the ordinal number of a calendar week within the year.
Example: Week number one year 2000 (i.e. 2000-01-03/09), is written 2000W01 or 2000-W01.

Annotation 6:
Although it is acceptable in ISO 8601 to identify days by means of year, week numbers and day numbers within the week, this is totally unnecessary as all days can be denoted by dates in the sequence year, month and day. Furthermore, to number weeks is rarely used outside Scandinavia and Germany.
(It is also acceptable in ISO 8601 to identify days by means of year and ordinal day number within the year, without respect to the division of year into months.)

Annotation 7:
ANSI does not have a standard for numbering the weeks of a year.

CONCLUSION

Any space of time or any point of time can be effectively and universally specified by using the ISO 8601 standard.

For further details:
ISO www.iso.ch;
SIS www.sis.se;
ITS www.its.se;
CEN www.cenorm.be;
ANSI www.ansi.org

 

Eskilstuna in April1999
© Kent Lund