Calendar date

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A date in a calendar is a reference to a particular day by means of a calendar system. The calendar date allows the particular day to be identified. A person can often determine how many days a particular date comes after another date. For example, "19 February 2003" is ten days after "9 February 2003" in the Gregorian calendar.

The date of a particular event depends on the time zone being used. For example the attack on Pearl Harbor took place on 7 December 1941, in Hawaii, but on 8 December in Japan.

A designated date may be used by another calendar to refer to another day as in the Gregorian calendar and in the Julian calendar, which have been used simultaneously in different places.

In most calendar systems, the date consists of three parts: the day of month, month, and the year. There may also be additional parts, such as the day of week. Years are usually counted from a particular starting point, usually called the epoch, with era referring to the particular period of time. (Note the different use of the terms in geology.) The most widely used epoch is a conventional birthdate of Jesus (which was established by Dionysius Exiguus in the sixth century).

A date without the year part may also be referred to as a date or calendar date (such as "9 February" rather than "9 February 2003"). As such, it defines the days of an annual event, such as a birthday or Christmas on 25 December.

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[edit] Giving dates in spoken English

A date written as 7 December is pronounced "the seventh of December", while December 7 is called "December seventh", or "December the seventh". "December seventh" is preferred by Americans.

[edit] Date format

Related to the classification of a day as a specific calendar date is the format used to express that date. The differing formats of dates are an example of endianness.

Even for any specific calendar system, different formats are used. For example, the following formats all express the same date in the Gregorian calendar:

[edit] Little endian forms, starting with the day

This sequence is common to the vast majority of the world's countries.[citation needed]

  • 16/11/2003, 16.11.2003, 16-11-2003 or 16-11-03
  • 16th of November 2003
  • 16th November 2003
  • 16 November 2003
  • 16 Nov 2003

[edit] Big endian forms, starting with the year

This form is consistent with the endianness of the western decimal numbering system, progressing from the highest to the lowest order magnitude.

  • 2003 November 16
  • 2003-11-16: the ISO 8601 International formal standard ordering for dates, often formatted to be especially easily read and sorted by computers. It is used with UTC in the Internet date/time format (see the external link below). This format is also favoured in certain Asian countries, mainly East Asian countries, as well as in most Middle and East European countries like Romania or Hungary. The big endian convention is also frequently used in Canada, but all three conventions are used there.[1]

[edit] Middle endian forms, starting with the month

This sequence is common to a smaller number of countries.

  • November 16, 2003
  • Nov. 16, 2003
  • 11/16/2003, 11-16-2003, 11.16.2003 or 11.16.03

This order is used in the United States and countries with U.S. influence (but the U.S. federal government sometimes uses day, month, year). Britain originally used day, month, year, then for a short while used month, day, year, and finally reverted to the original form (day, month, year) which was revived around 1900; the USA chose to stick with month, day, year, but did originally use day, month, year as the British did.

[edit] Usage issues

The many numerical forms can create confusion when used in international correspondence, particularly when abbreviating the year to its final two digits.

When numbers are used to represent months, a significant amount of confusion can arise from the ambiguity of a date order; especially when the numbers representing the day, month or year are low, it can be impossible to tell which order is being used. This can be clarified by using four digits to represent years, and naming the month; for example, "Feb" instead of "02". In some countries Roman numerals are used to denote the month, e.g. 11.IX.2001. Many Internet sites use year/month/day, and those using other conventions often write out the month (9-MAY-2001, MAY 09 2001, etc.) so there is no ambiguity. The ISO 8601 date order, with four-digit years, is specifically chosen to be unambiguous.

The ISO 8601 standard also has the advantage of being language independent and therefore is useful when there may be no language context and a universal application is desired (expiration dating on export products, for example). Another advantage is that a plain text list of dates with this format can be easily sorted by word processors, spreadsheets and other software tools with built-in sorting functions.

At least in the United States, dates are rarely written in purely numerical forms in formal writing.

Mixed units, for example feet and inches, or pounds and ounces, are normally written with the largest unit first, in decreasing order. Numbers are also written in that order, so the digits of 2006 indicate, in order, the millennium, the century within the millennium, the decade within the century, and the year within the decade. The only date order that is consistent with these well established conventions is year-month-day.

An early U.S. Federal Information Processing Standard recommended 2-digit years. This is now widely recognized as a bad idea. Even some U.S. government agencies now use ISO 8601 with 4 digit years [2][3].

When transitioning from one date notation to another, people often write both Old Style and New Style dates.

[edit] dd/mm/yyyy (day, month, year)

Using the dd/mm/yyyy format, the 30th of December 2006 would be written as 30/12/2006.

The dd/mm/yyyy format is used by:

Note that '9/11' can refer to both 'The fall of the Berlin Wall' on 9 November 1989 and to the 11 September 2001 attacks on the World Trade Center in the USA. '9/11' may also refer to the Chilean coup of 1973.

Note also that in the United Kingdom, while it is regarded as acceptable, but rare, to write monthname, day, year (as well as the little endian day, monthname, year), this order is unacceptable when written numerically.

[edit] yyyy-mm-dd (year, month, day) - the ISO 8601 standard

Using the yyyy-mm-dd format, the 30th of December 2006 would be written as 2006-12-30.

The ISO 8601 standard, yyyy-mm-dd, is used by:

It is often used in scientific, technical or international communication.

[edit] Alphabetical ordering advantages

One of the advantages of using the ISO 8601 standard date format is that it when dates in this format are ordered 'alphabetically' this also orders them in date order e.g. -

  • 1998-02-28 (28 February 1998 - earliest date in the list)
  • 1999-03-01 (1 March 1999 - middle date in the list)
  • 2000-01-30 (30 January 2000 - latest date in the list)

Using the MM-DD-YYYY format, alphabetically ordering the files would put them out of date order:

  • 01-30-2000 (30 January 2000 - latest date in the list)
  • 02-28-1998 (28 February 1998 - earliest date in the list)
  • 03-01-1999 (1 March 1999 - middle date in the list)

Using the DD-MM-YYYY format, alphabetically ordering the files would also put them out of date order:

  • 01-03-1999 (1 March 1999 - middle date in the list)
  • 28-02-1998 (28 February 1998 - earliest date in the list)
  • 30-01-2000 (30 January 2000 - latest date in the list)

[edit] yyyy-mmm-dd (year, month, day)

Using the yyyy-mmm-dd format, the 30th of December 2006 would be written as 2006-Dec-30.

The yyyy-mmm-dd format is used by:

[edit] m/d/y (month, day, year)

Using the m/d/y format, the 30th of December 2006 would be written as 12/30/06. Note that leading zeroes in the month and day are often dropped; for example, the 1st of April 2006 would often be written as 4/1/06.

The m/d/y format is used by:

[edit] Day and year only

The U.S. military sometimes uses a system that indicates the year and day, but not the month. For example, "10 December 1999" can be written in some contexts as "1999345", for the 345th day of 1999.[1] This system is most often used on forms.

See also: calendar, time, date-time group, Japanese calendar, Wikibooks:English:Time

[edit] Week number used

Companies in Europe often use year, week number and day for planning purposes. Since a week is a fundamental unit for working life, it makes sense. An event in a project can happen, for example, on w43, w0543 or w543 (week 43 year 2005) or even w43-1 (Monday week 43 year 2005). One problem is that week numbering has different standards, for example the ISO week date, not used by the USA.

[edit] References

  1. ^ Kuhn, Markus, A summary of the international standard date and time notation, University of Cambridge Computer Laboratory, last modified 2004-December 19. Accessed 2006-August 1.

[edit] See also

[edit] External links

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