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63-588: ISO 8601 is an international standard covering the worldwide exchange and communication of date and time -related data. It is maintained by the International Organization for Standardization (ISO) and was first published in 1988, with updates in 1991, 2000, 2004, and 2019, and an amendment in 2022. The standard provides a well-defined, unambiguous method of representing calendar dates and times in worldwide communications, especially to avoid misinterpreting numeric dates and times when such data
126-547: A comma or a dot on the baseline , is used as a separator between the time element and its fraction. (Following ISO 80000-1 according to ISO 8601:1-2019, it does not stipulate a preference except within International Standards, but with a preference for a comma according to ISO 8601:2004.) For example, to denote "14 hours, 30 and one half minutes", do not include a seconds figure; represent it as "14:30,5", "T1430,5", "14:30.5", or "T1430.5". There
189-409: A comma or a full stop , as in "P0,5Y" or "P0.5Y". The standard does not prohibit date and time values in a duration representation from exceeding their "carry over points" except as noted below. Thus, "PT36H" could be used as well as "P1DT12H" for representing the same duration. But keep in mind that "PT36H" is not the same as "P1DT12H" when switching from or to Daylight saving time . Alternatively,
252-531: A bit within their industries. Joseph Whitworth 's screw thread measurements were adopted as the first (unofficial) national standard by companies around the country in 1841 . It came to be known as the British Standard Whitworth , and was widely adopted in other countries. By the end of the 19th century differences in standards between companies were making trade increasingly difficult and strained. The Engineering Standards Committee
315-410: A book written in 2019 by Nicholas Rich and Tegwen Malik gives a very comprehensive overview of the history of standards, how ISO standards are drafted along with key ISO standards such as ISO 9001 and ISO 14001. A paper has been published explaining the differences between international standards and private standards . One of the most well established international standardization organizations
378-556: A commission to oversee the process. By 1906 , his work was complete and he drew up a permanent constitution for the first international standards organization, the International Electrotechnical Commission (IEC). The body held its first meeting that year in London , with representatives from 14 countries. In honour of his contribution to electrical standardisation, Lord Kelvin was elected as
441-489: A complete date expression, the letter "T" as a delimiter, and a valid time expression. For example, "2007-04-05T14:30" . In ISO 8601:2004 it was permitted to omit the "T" character by mutual agreement as in "200704051430" , but this provision was removed in ISO ;8601-1:2019. Separating date and time parts with other characters such as space is not allowed in ISO 8601, but allowed in its profile RFC 3339. If
504-407: A format for duration based on combined date and time representations may be used by agreement between the communicating parties either in the basic format PYYYYMMDDThhmmss or in the extended format P[YYYY]-[MM]-[DD]T[hh]:[mm]:[ss] . For example, the first duration shown above would be "P0003-06-04T12:30:05" . However, individual date and time values cannot exceed their moduli (e.g. a value of 13 for
567-507: A four-digit year, 0000 through 9999. [MM] indicates a two-digit month of the year, 01 through 12. [DD] indicates a two-digit day of that month, 01 through 31. For example, "5 April 1981" may be represented as either "1981-04-05" in the extended format or "19810405" in the basic format . The standard also allows for calendar dates to be written with reduced precision. For example, one may write "1981-04" to mean "1981 April". One may simply write "1981" to refer to that year, "198" to refer to
630-545: A large user base, doing some well established thing that between them is mutually incompatible. Establishing international standards is one way of preventing or overcoming this problem. To support this, the World Trade Organization (WTO) Technical Barriers to Trade (TBT) Committee published the "Six Principles" guiding members in the development of international standards. The implementation of standards in industry and commerce became highly important with
693-492: A positive UTC offset describes a time zone east of the prime meridian where the civil time is ahead of UTC . So the zone designation for Cairo will be "+02:00","+0200", or "+02". A time zone where the civil time coincides with UTC is always designated as positive, though the offset is zero (see related specifications below). So the zone designation for London (on standard time ) would be " +00:00 ", " +0000 ", or " +00 ". See List of UTC offsets for other UTC offsets . It
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#1732772476554756-457: A proposal to form a new global standards body. In October 1946 , ISA and UNSCC delegates from 25 countries met in London and agreed to join forces to create the International Organization for Standardization (ISO); the organization officially began operations in February 1947 . Global standards are also referred to as industry or private standards , which are designed and developed with
819-423: A time zone designator is required, it follows the combined date and time. For example, "2007-04-05T14:30Z" or "2007-04-05T12:30−02:00" . Either basic or extended formats may be used, but both date and time must use the same format. The date expression may be calendar, week, or ordinal, and must use a complete representation. The time may be represented using a specified reduced precision format. Durations define
882-507: Is an ordinal format for the multiples of a day elapsed since the start of year. It is represented as "YYYY-DDD" (or YYYYDDD), where [YYYY] indicates a year and [DDD] is the "day of year", from 001 through 365 (366 in leap years ). For example, "1981-04-05" is the same as "1981-095" . This simple form is preferable for occasions when the arbitrary nature of week and month definitions are more of an impediment than an aid, for instance, when comparing dates from different calendars. This format
945-488: Is appended directly to the time instead of "Z" suffix above; other nautical time zone letters are not used. The offset is applied to UTC to get the civil time in the designated time zone in the format '±[hh]:[mm]', '±[hh][mm]', or '±[hh]'. A negative UTC offset describes a time zone west of the prime meridian where the civil time is behind UTC. So the zone designation for New York (on standard time ) would be "−05:00","−0500", or "−05". Conversely,
1008-433: Is given with a time representation, the time is assumed to be in local time. While it may be safe to assume local time when communicating in the same time zone, it is ambiguous when used in communicating across different time zones. Even within a single geographic time zone, some local times will be ambiguous if the region observes daylight saving time . It is usually preferable to indicate a time zone (zone designator) using
1071-527: Is no limit on the number of decimal places for the decimal fraction. However, the number of decimal places needs to be agreed to by the communicating parties. For example, in Microsoft SQL Server, the precision of a decimal fraction is 3 for a DATETIME, i.e., "yyyy-mm-ddThh:mm:ss[.mmm]". Time zones in ISO 8601 are represented as local time (with the location unspecified), as UTC , or as an offset from UTC. If no UTC relation information
1134-431: Is not a valid representation for a duration of 0 seconds. "PT0S" or "P0D", however, are both valid and represent the same duration. To resolve ambiguity, "P1M" is a one-month duration and "PT1M" is a one-minute duration (note the time designator, T, that precedes the time value). The smallest value used may also have a decimal fraction, as in "P0.5Y" to indicate half a year. This decimal fraction may be specified with either
1197-420: Is not permitted to state a zero value time offset with a negative sign, as "−00:00", "−0000", or "−00". The section dictating sign usage states that a plus sign must be used for a positive or zero value, and a minus sign for a negative value. A plus-minus-sign ( ± ) may also be used if it is available. Contrary to this rule, RFC 3339, which is otherwise a profile of ISO 8601, permits
1260-515: Is produced by extending the Gregorian calendar backward to the dates preceding its official introduction in 1582. In nations that adopted the Gregorian calendar after its official and first introduction, dates occurring in the interim period of 15 October 1582 (the first date of use of Gregorian calendrical dates, being dated 5 October 1582 in the preceding Julian calendar ) to the date on which
1323-531: Is sometimes used in computer software to simplify identifying pre-Gregorian dates, e. g. in PostgreSQL , MySQL , SQLite , PHP , CIM , Delphi and Python . Before the official and first introduction of the Gregorian calendar, the differences between Julian and proleptic Gregorian calendar dates are as follows: The table below assumes a Julian leap day of 29 February, but the Julian leap day, that is,
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#17327724765541386-744: Is the International Telecommunication Union (ITU), a specialized agency of the United Nations which was founded on 17 May 1865 as the International Telegraph Union. The ITU was initially focused on the standardization of telegraph signals, and later evolved to include telephony , radio and satellite communications, and other information and communication technology . By the mid to late 19th century , efforts were being made to standardize electrical measurement. An important figure
1449-408: Is the weekday number , from 1 through 7, beginning with Monday and ending with Sunday. There are several mutually equivalent and compatible descriptions of week 01: As a consequence, if 1 January is on a Monday, Tuesday, Wednesday or Thursday, it is in week 01. If 1 January is on a Friday, Saturday or Sunday, it is in week 52 or 53 of the previous year (there is no week 00). 28 December is always in
1512-482: Is to cite the date as expressed in the original text and to notate any contextual implications and conclusions regarding the calendar used and equivalents in other calendars. This practice permits others to re-evaluate the original evidence. For these calendars one can distinguish two systems of numbering years BC. Bede and later historians did not enumerate any year as zero ( nulla in Latin; see Year zero ); therefore
1575-435: Is transferred between countries with different conventions for writing numeric dates and times. ISO 8601 applies to these representations and formats: dates , in the Gregorian calendar (including the proleptic Gregorian calendar); times , based on the 24-hour timekeeping system , with optional UTC offset ; time intervals ; and combinations thereof. The standard does not assign specific meaning to any element of
1638-574: Is used to designate the Zulu time zone . However the ACP 121 standard that defines the list of military time zones makes no mention of UTC and derives the "Zulu time" from the Greenwich Mean Time which was formerly used as the international civil time standard. GMT is no longer precisely defined by the scientific community and can refer to either UTC or UT1 depending on context. The UTC offset
1701-449: Is used with simple hardware systems that have a need for a date system, but where including full calendar calculation software may be a significant nuisance. This system is sometimes referred to as "Julian Date", but this can cause confusion with the astronomical Julian day , a sequential count of the number of days since day 0 beginning 1 January 4713 BC Greenwich noon, Julian proleptic calendar (or noon on ISO date −4713-11-24 which uses
1764-481: The International Telecommunication Union (ITU) and the International Electrotechnical Commission (IEC). Together, these three organizations have formed the World Standards Cooperation alliance. International standards can be applied directly or adapted to meet local conditions. When adopted, they lead to the creation of national standards that are either equivalent to or largely align with
1827-480: The Julian calendar would be contrary to the standard (because at the switchover date, the dates would not be consecutive). ISO 8601 prescribes, as a minimum, a four-digit year [YYYY] to avoid the year 2000 problem . It therefore represents years from 0000 to 9999, year 0000 being equal to 1 BC and all others AD , similar to astronomical year numbering . However, years before 1583 (the first full year following
1890-518: The decade from 1980 to 1989 inclusive, or "19" to refer to the century from 1900 to 1999 inclusive. Although the standard allows both the "YYYY-MM-DD" and YYYYMMDD formats for complete calendar date representations, if the day [DD] is omitted then only the YYYY-MM format is allowed. By disallowing dates of the form YYYYMM, the standard avoids confusion with the truncated representation YYMMDD (still often used). The 2000 version also allowed writing
1953-466: The Gregorian calendar year that is ending; if three, they are Monday, Tuesday and Wednesday. Similarly, the last ISO week of a year may have up to three days that are actually in the Gregorian calendar year that is starting; if three, they are Friday, Saturday, and Sunday. The Thursday of each ISO week is always in the Gregorian calendar year denoted by the ISO week-numbering year. Examples: An ordinal date
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2016-628: The Gregorian calendar, Washington's birthday was dated 22 February 173 2 proleptically, according to the Gregorian calendar applied backward. This remains the modern dating of his birthday. ISO 8601 :2004 (clause 3.2.1 The Gregorian calendar) explicitly requires use of the proleptic Gregorian calendar for all dates before the introduction of 15 October 1582, if the partners to an exchange of information agree. Most scholars of Maya civilization also use it, especially when converting Long Count dates (1st century BC – 10th century AD). The best practice for citation of historically contemporary documents
2079-414: The Gregorian proleptic calendar with a year 0000). ISO 8601 uses the 24-hour clock system. As of ISO 8601-1:2019, the basic format is T[hh][mm][ss] and the extended format is T[hh]:[mm]:[ss]. Earlier versions omitted the T (representing time) in both formats. So a time might appear as either "T134730" in the basic format or "T13:47:30" in the extended format . ISO 8601-1:2019 allows
2142-481: The T to be omitted in the extended format, as in "13:47:30", but only allows the T to be omitted in the basic format when there is no risk of confusion with date expressions. Either the seconds, or the minutes and seconds, may be omitted from the basic or extended time formats for greater brevity but decreased precision; the resulting reduced precision time formats are: As of ISO 8601-1:2019/Amd 1:2022, "00:00:00" may be used to refer to midnight corresponding to
2205-489: The amount of intervening time in a time interval and are represented by the format P[n]Y[n]M[n]DT[n]H[n]M[n]S or P[n]W as shown on the aside. In these representations, the [n] is replaced by the value for each of the date and time elements that follow the [n]. Leading zeros are not required, but the maximum number of digits for each element should be agreed to by the communicating parties. The capital letters P , Y , M , W , D , T , H , M , and S are designators for each of
2268-513: The body's first President. The International Federation of the National Standardizing Associations (ISA) was founded in 1926 with a broader remit to enhance international cooperation for all technical standards and specifications. The body was suspended in 1942 during World War II . After the war, ISA was approached by the recently formed United Nations Standards Coordinating Committee (UNSCC) with
2331-538: The character set has a minus sign, such as U+2212 − MINUS SIGN in Unicode , then that character should be used. The HTML character entity invocation for − is − . ISO 8601-2:2019 allows for general durations for time offsets. For example, more precision can be added to the time offset with the format '<time>±[hh]:[mm]:[ss].[sss]' or '<time>±[n]H[n]M[n]S' as below. A single point in time can be represented by concatenating
2394-488: The date and time elements and are not replaced. For example, "P3Y6M4DT12H30M5S" represents a duration of "three years, six months, four days, twelve hours, thirty minutes, and five seconds". Date and time elements including their designator may be omitted if their value is zero, and lower-order elements may also be omitted for reduced precision. For example, "P23DT23H" and "P4Y" are both acceptable duration representations. However, at least one element must be present, thus "P"
2457-504: The dates/times represented: the meaning of any element depends on the context of its use. Dates and times represented cannot use words that do not have a specified numerical meaning within the standard (thus excluding names of years in the Chinese calendar ), or that do not use computer characters (excludes images or sounds). In representations that adhere to the ISO 8601 interchange standard , dates and times are arranged such that
2520-453: The entire world in mind. Unlike international standards, these standards are not developed in international organizations or standards setting organizations (SSO) which follow a consensus process. Instead, these standards are developed by private sector entities, like NGOs and for-profit organizations, often without transparency, openness, or consensus considerations. Proleptic Gregorian calendar The proleptic Gregorian calendar
2583-584: The fourth revision of the standard ISO 8601-1:2019 represents slightly updated contents of the previous ISO 8601:2004 standard, whereas the new ISO 8601-2:2019 defines various extensions such as uncertainties or parts of the Extended Date/Time Format (EDTF). An amendment was published in October 2022 featuring minor technical clarifications and attempts to remove ambiguities in definitions. The most significant change, however,
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2646-517: The greatest temporal term (typically a year) is placed at the left and each successively lesser term is placed to the right of the previous term. Representations must be written in a combination of Arabic numerals and the specific computer characters (such as "‐", ":", "T", "W", "Z") that are assigned specific meanings within the standard; that is, such commonplace descriptors of dates (or parts of dates) as "January", "Thursday", or "New Year's Day" are not allowed in interchange representations within
2709-446: The instant at the beginning of a calendar day; and "24:00:00" to refer to midnight corresponding to the instant at the end of a calendar day. ISO 8601-1:2019 as originally published removed "24:00:00" as a representation for the end of day although it had been permitted in earlier versions of the standard. A decimal fraction may be added to the lowest order time element present in any of these representations. A decimal mark , either
2772-433: The international standard date system, ISO 8601. In these systems, the year 0 is a leap year. Although the nominal Julian calendar began in 45 BC, leap years between 45 BC and 1 BC were irregular (see Leap year error ). Thus the Julian calendar with quadrennial leap years was only used from the end of AD 4 until 1582 or later (contingent on the specific nation in question). The proleptic Gregorian calendar
2835-432: The international standards in technical content, though they may have: (i) editorial variations, such as differences in appearance, the use of symbols, measurement units, or the choice of a point over a comma as the decimal marker, and (ii) variations arising from conflicts with government regulations or industry-specific requirements, which may be influenced by factors such as climate, geography, technology, infrastructure, or
2898-408: The introduction of the Gregorian calendar ) are not automatically allowed by the standard. Instead, the standard states that "values in the range [0000] through [1582] shall only be used by mutual agreement of the partners in information interchange". To represent years before 0000 or after 9999 , the standard also permits the expansion of the year representation but only by prior agreement between
2961-594: The lack of efficiency in this system and began to consider proposals for an international standard for electric engineering. In 1904 , Crompton represented Britain at the Louisiana Purchase Exposition in St. Louis as part of a delegation by the Institute of Electrical Engineers . He presented a paper on standardisation, which was so well received that he was asked to look into the formation of
3024-513: The last week of its year. The week number can be described by counting the Thursdays: week 12 contains the 12th Thursday of the year. The ISO week-numbering year starts at the first day (Monday) of week 01 and ends at the Sunday before the new ISO year (hence without overlap or gap). It consists of 52 or 53 full weeks. The first ISO week of a year may have up to three days that are actually in
3087-451: The month or 25 for the hour would not be permissible). International standard An international standard is a technical standard developed by one or more international standards organizations . International standards are available for consideration and use worldwide. The most prominent such organization is the International Organization for Standardization (ISO). Other prominent international standards organizations including
3150-533: The onset of the Industrial Revolution and the need for high-precision machine tools and interchangeable parts . Henry Maudslay developed the first industrially practical screw-cutting lathe in 1800, which allowed for the standardisation of screw thread sizes for the first time. Maudslay's work, as well as the contributions of other engineers, accomplished a modest amount of industry standardization ; some companies' in-house standards spread
3213-432: The pertinent nation adopted the Gregorian calendar and abandoned the Julian calendar are sometimes 'Gregorianized' also. For example, the birthday of U.S. President George Washington was originally dated 11 February 173 1 ( Old Style ) because Great Britain , of which he was born a subject, used (until September 1752) the Julian calendar and dated the beginning of English years as 25 March. After Great Britain switched to
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#17327724765543276-399: The safety standards deemed necessary by the relevant authorities. International standards are one way to overcome technical barriers in international commerce caused by differences among technical regulations and standards developed independently and separately by each nation, national standards organization, or business. Technical barriers arise when different groups come together, each with
3339-423: The sender and the receiver. An expanded year representation [± Y YYYY] must have an agreed-upon number of extra year digits beyond the four-digit minimum, and it must be prefixed with a + or − sign instead of the more common AD/BC (or CE/BCE ) notation; by convention 1 BC is labelled +0000 , 2 BC is labeled −0001, and so on. Calendar date representations are in the form shown in the adjacent box. [YYYY] indicates
3402-456: The standard's notation. If the time is in UTC , add a Z directly after the time without a space. Z is the zone designator for the zero UTC offset. "09:30 UTC" is therefore represented as "09:30Z" or "T0930Z". "14:45:15 UTC" would be "14:45:15Z" or "T144515Z". The Z suffix in the ISO 8601 time representation is sometimes referred to as "Zulu time" or "Zulu meridian" because the same letter
3465-533: The standard. The first edition of the ISO 8601 standard was published as ISO 8601:1988 in 1988. It unified and replaced a number of older ISO standards on various aspects of date and time notation: ISO 2014 , ISO 2015 , ISO 2711 , ISO 3307 , and ISO 4031 . It has been superseded by a second edition ISO 8601:2000 in 2000, by a third edition ISO 8601:2004 published on 1 December 2004, and withdrawn and revised by ISO 8601-1:2019 and ISO 8601-2:2019 on 25 February 2019. ISO 8601
3528-478: The truncation "--04-05" to mean "April 5" but the 2004 version does not allow omitting the year when a month is present. Examples: Week date representations are in the formats as shown in the adjacent box. [YYYY] indicates the ISO week-numbering year which is slightly different from the traditional Gregorian calendar year (see below). [Www] is the week number prefixed by the letter W , from W01 through W53. [D]
3591-435: The use of "−00" with the same denotation as "+00" but a differing connotation: an unknown UTC offset . To represent a negative offset, ISO 8601 specifies using a minus sign ( − ) . If the interchange character set is limited and does not have a minus sign character, then the hyphen-minus should be used, ( - ). ASCII does not have a minus sign, so its hyphen-minus character (code 45 10 ) would be used. If
3654-441: The year preceding AD 1 is 1 BC. In this system the year 1 BC is a leap year (likewise in the proleptic Julian calendar ). Mathematically, it is more convenient to include a year 0 and represent earlier years as negative numbers for the specific purpose of facilitating the calculation of the number of years between a negative (BC) year and a positive (AD) year. This is the convention in astronomical year numbering and
3717-512: Was R. E. B. Crompton , who became concerned by the large range of different standards and systems used by electrical engineering companies and scientists in the early 20th century . Many companies had entered the market in the 1890s and all chose their own settings for voltage , frequency , current and even the symbols used on circuit diagrams. Adjacent buildings would have totally incompatible electrical systems simply because they had been fitted out by different companies. Crompton could see
3780-764: Was established in London in 1901 as the world's first national standards body. After the First World War , similar national bodies were established in other countries. The Deutsches Institut für Normung was set up in Germany in 1917 , followed by its counterparts, the American National Standard Institute and the French Commission Permanente de Standardisation , both in 1918 . There are not many books that cover standards in general, but
3843-494: Was prepared by, and is under the direct responsibility of, ISO Technical Committee TC 154. ISO 2014, though superseded, is the standard that originally introduced the all-numeric date notation in most-to-least-significant order [YYYY]-[MM]-[DD] . The ISO week numbering system was introduced in ISO 2015, and the identification of days by ordinal dates was originally defined in ISO 2711. Issued in February 2019,
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#17327724765543906-425: Was removed in ISO 8601-1:2019). However, ISO calendar dates before the convention are still compatible with the Gregorian calendar all the way back to the official introduction of the Gregorian calendar on 15 October 1582. Earlier dates, in the proleptic Gregorian calendar , may be used by mutual agreement of the partners exchanging information. The standard states that every date must be consecutive, so usage of
3969-522: Was the reintroduction of the "24:00:00" format to refer to the instant at the end of a calendar day. The standard uses the Gregorian calendar , which "serves as an international standard for civil use". ISO 8601:2004 fixes a reference calendar date to the Gregorian calendar of 20 May 1875 as the date the Convention du Mètre ( Metre Convention ) was signed in Paris (the explicit reference date
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