Calendar date

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A date in a calendar is a reference to a particular day represented within a calendar system. The calendar date allows the specific day to be identified. The number of days between two dates may be calculated. For example, "19 June 2008" is ten days after "9 June 2008" in the Gregorian calendar. The date of a particular event depends on the time zone in which it occurs. For example the attack on Pearl Harbor took place on December 7, 1941, in Hawaii, but on December 8 in Japan.

A particular day may be represented by a different date in another calendar as in the Gregorian calendar and 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 "10 June" rather than "10 June 2008"). As such, it defines the day of an annual event, such as a birthday or Christmas on 25 December.

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[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 a 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 (see below for breakdown of countries by format). This date format originates from the custom of writing the date as ' the 16th day of November in the year of our Lord 2003' in religious and legal documents which at one time were the majority of documents created. The format has shortened as more and more people learned to read and write but the order of the elements has remained constant.

  • 16/11/2003, 16.11.2003 (using dot as separator with this sequence has been defined by DIN 5008), 16-11-2003 or 16-11-03
  • 16th [of] November 2003 (The 'of' is included in speech, however it is considered bad practice to include it when written.)
  • 16th November 2003
  • 16 November 2003
  • 16 Nov 2003

[edit] Big endian forms, starting with the year

This form is consistent with the big endianness of the western decimal numbering system, progressing from the highest to the lowest order magnitude. This is a standard format in Asian countries where the most significant data item is written first followed by lesser data items. An example of this is the custom of writing the family name before the personal name of an individual.

  • 2003 November 16
  • 2003-11-16: the ISO 8601 international standard orders the components of a date like this, and additionally uses leading zeros, e.g. 0813-03-01, to be 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 some Middle and East European countries like 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 used exclusively only in the United States and two other small pacific countries that have been heavily influenced by the US.

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

[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.

For example, '9/11' can refer to both 'The fall of the Berlin Wall' on 9 November 1989 and to the September 11, 2001 attacks on the World Trade Center in the USA. In the United States, dates are rarely written in purely numerical forms in formal writing. In the United Kingdom, while it is regarded as acceptable, but rare, to write monthname day, year (as well as day monthname year), this order is never used when written numerically, although the American shorthand "9/11" is widely understood as referring to the 11 September terrorist attacks.[2]

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.[citation needed] 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 is therefore useful when there may be no language context and a universal application is desired (expiration dating on export products, for example).

In addition, the ISO considers its ISO 8601 standard to make sense from a logical perspective.[3] 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. 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.

An early U.S. Federal Information Processing Standard recommended 2-digit years. This is now widely recognized as a bad idea, because of the year 2000 problem. Some U.S. government agencies now use ISO 8601 with 4 digit year.[4][5]

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

     dd/mm/yyyy      dd/mm/yyyy and yyyy/mm/dd      yyyy/mm/dd      mm/dd/yyyy      mm/dd/yyyy and dd/mm/yyyy      mm/dd/yyyy,dd/mm/yyyy,yyyy/mm/dd
     dd/mm/yyyy      dd/mm/yyyy and yyyy/mm/dd      yyyy/mm/dd      mm/dd/yyyy      mm/dd/yyyy and dd/mm/yyyy      mm/dd/yyyy,dd/mm/yyyy,yyyy/mm/dd

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

Using the dd/mm/yyyy format, the 30th December 2006 would be written as 30/12/2006. The dd/mm/yyyy format is used in:

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

Using the mm/dd/yy format, December 30, 2006 would be written as 12/30/06.

The mm/dd/yy format is used in:

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

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

  • Used internationally in some contexts as the ISO 8601 standard
  • Canada (yyyy-mm-dd) (All 3 main types are used in Canada- in French and in English)
  • China (yyyy-mm-dd or yyyy年m月d日)
  • Denmark (The format dd-mm-yy(yy) is the traditional Danish date format. The international format yyyy-mm-dd or yyyymmdd is also accepted. There are no preferences, although the traditional format is the most widely used. The formats dd.'monthname' yyyy and in handwriting d/m/yy are also acceptable. [6])
  • Europe[7]
  • Hong Kong (same as China)
  • Hungary (yyyy.mm.dd – traditionally the number of the month is most often written in Roman numerals)
  • Japan, often in the form yyyy年m月d日; sometimes Japanese era year is used, e.g. 平成18年12月30日.
  • Korea (yyyy년 mm월 dd일)
  • Latvia (But often dd.mm.yyyy. is used)
  • Lithuania (yyyy-mm-dd)
  • Macau (same as China)
  • Middle East
  • Mongolia (yyyy-mm-dd)
  • Nepal
  • South Africa ("d/m/yy" is a common alternative)
  • Sweden
  • Taiwan; same as China except year might be represented using ROC era system: 民國95年12月30日.

[edit] Advantages for Ordering in Sequence

One of the advantages of using the ISO 8601 standard date format is that when dates in this format are ordered sequentially by the leading number, this also orders them in date order, e.g.:

1998-02-28 (28 February 1998)
1999-03-01 (01 March    1999)
2000-01-30 (30 January  2000)

Using the MM-DD-YYYY format, sequential ordering by the leading number would put a list out of date order (as it would be the months being ordered regardless of year):

01-30-2000 (30 January  2000)
02-28-1998 (28 February 1998) 
03-01-1999 (01 March    1999)

Using the DD-MM-YYYY format, sequential ordering by the leading number would also put a list out of date order (as it would be the day being ordered regardless of year or month):

01-03-1999 (01 March    1999) 
28-02-1998 (28 February 1998) 
30-01-2000 (30 January  2000)

The Sequence Ordering is often used in scientific, technical or international communication.

[edit] Day and year only

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

The U.S. military sometimes uses a system, which they call "Julian date format"[8] that indicates the year and the actual day out of the 365 days of the year (and thus a designation of the month would not be needed). For example, "10 December 1999" can be written in some contexts as "1999345" or "99345", for the 345th day of 1999.[9] This system is most often used in US military logistics, since it makes the process of calculating estimated shipping and arrival dates easier. For example: say a tank engine takes an estimated 35 days to ship by sea from the US to Korea. If the engine is sent on 99104, it should arrive on 99139. Note that outside of the US military, this format is usually referred to as "ordinal date", rather than "Julian date."

Such ordinal date formats are also used by many computer programs (especially those for mainframe systems). Using a three-digit Julian day number saves one byte of computer storage over a two-digit month plus two-digit day, e.g. "January 17" is 017 in Julian versus 0117 in month-day format.

Another "ordinal" date system ("ordinal" in the sense of advancing in value by one as the date advances by one day) is in common use in astronomical calculations and referencing and uses the same name as this "logistics" system. The continuity of representation of period regardless of the time of year being considered is obviously highly useful to both groups of specialists. The astronomers describe their system too as being a "Julian date", and it is described in more detail in the article Julian date. Unlike the system described above, the astronomical system does not consider years, it only counts days. Thus it is unperturbed by complications such as leap years.

[edit] Week number used

Companies in Europe often use year, week number and day for planning purposes. So, for example, an event in a project can happen on w43 (week 43) or w43-1 (Monday, week 43) or, if the year needs to be indicated, on w0543 or w543 (year 2005 week 43).

The ISO does present a standard for identifying weeks, but as it does not match up with Gregorian calendar (the beginning and ending days of a given year do not match up), this standard is somewhat more problematic than the other standards for dates.

[edit] Expressing dates in spoken English

In British English, full dates are usually written and spoken as 7th December 2007 (or 7 December 2007) and pronounced "the seventh of December", with the occasional usage of December 7, 2007 ("December the seventh, 2007"). In common with continental European usage, however, numerical dates are invariably ordered dd/mm/yyyy.

In the United States, the usual written form is December 7, pronounced "December (the) seventh" or colloquially "December seven".

[edit] See also

[edit] References

  1. ^ Canadian Payments Association - Specifications for Imageable Cheques and Other Payment Items
  2. ^ BBC News - America's Day of Terror" (Example of British website using "9/11" shorthand)
  3. ^ Numeric representation of Dates and Time. Retrieved on 2008-04-27.
  4. ^ http://www.nyecounty.net/iso8601.html
  5. ^ International Standard Date and Time Notation
  6. ^ a b The Danish language advisory committee
  7. ^ http://ec.europa.eu/food/food/biosafety/salmonella/data_dictionary_pigs_en.pdf
  8. ^ Hynes, John, A summary of time formats and standards. Accessed 2007-Mar 16.
  9. ^ 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] External links