Help:Dates
Wikidata offers a series of properties with datatype time, which allow storage of basic information defining single point in time. Time datatype can be further expanded with custom qualifiers to allow great range of possible time expressions. Adding and querying dates may seem simple, but available precision and changing calendars add complexity.
Model
[edit]Time datatype
[edit]- See also mw:Wikibase/DataModel/JSON#time
Page Special:ListDatatypes describes time datatype as
Literal data field for a point in time. Given as a date and time with some precision and boundaries. The time is saved internally in the specified calendar model.
- time – explicit value for point in time, represented as a timestamp resembling ISO 8601, e.g. +2013-01-01T00:00:00Z. The year is always signed and padded to have between 4 and 16 digits.
- timezone – explicit value as a signed integer. Timezone information as an offset from UTC in minutes.
- before – explicit integer value for how many units after the given time it could be. The unit is given by the precision.
- after – explicit integer value for how many units before the given time it could be. The unit is given by the precision.
- precision – explicit value encoded in a shortint. The numbers have the following meaning: 0 - billion years, 1 - hundred million years, ..., 6 - millennium, 7 - century, 8 - decade, 9 - year, 10 - month, 11 - day, 12 - hour, 13 - minute, 14 - second.
- calendarmodel – explicit value given as a URI. It identifies the calendar model of the timestamp.
That is an accurate description of the saved structure; however, much of it is not being used at the moment:
timefield can not be saved with precision higher than a "day".- We do not use
beforeandafterfields and use qualifiers instead to indicate time period. timezoneis also not used the encoding (Z) suggest UTC timezone (the date in London), but general practice on Wikidata is to save dates as reported in literature, which usually means in local timezone.calendar– explicit value defining calendar model. Currently two calendar models are supported: proleptic Gregorian calendar (Q1985727) and proleptic Julian calendar (Q1985786)
For example, the actual data structure of Adam Mickiewicz (Q79822)start time (P580) is
["P580"] = table {
table {
["datatype"] = "time",
["datavalue"] = table {
["type"] = "time",
["value"] = table {
["after"] = 0,
["before"] = 0,
["calendarmodel"] = "http://www.wikidata.org/entity/Q1985727",
["precision"] = 9,
["time"] = "+1838-01-01T00:00:00Z",
["timezone"] = 0,
},
},
["hash"] = "1438e02cdfc7ff91f7e722fbbf09f5ba5dba259b",
["property"] = "P580",
["snaktype"] = "value",
},
}
Precision
[edit]Below is a table with example time strings for several precision values. The strings can be accessed using Lua commands and are also used by QuickStatements (Q20084080)
.
The user interface interprets precision 7 (100 years) and 6 (1,000 years) using strict historical definitions of those terms, which starts with year ending with 01 and ends with year ending with 00. That might be counterintuitive to some people. When using the precision 7 or 6 it is safer to avoid years with the last digits 00. One option is to use the earliest year that avoids the problem, such as 2001 for the 3rd millennium. Another option is to use a date near the midpoint of the range, such as 1950 for the 20th century.
| precision | timestamp string | meaning | comments | |
|---|---|---|---|---|
| 11 | day | +2024-11-29T00:00:00Z
|
today's date | |
| 10 | month | +2024-11-00T00:00:00Z
|
this month | |
| 9 | year | +2024-00-00T00:00:00Z
|
current year | |
| 8 | decade | +2010-00-00T00:00:00Z
|
2010s | Any date in range 2010-2019 with precision 8 is interpreted as 2010s. |
| 7 | century | +1801-00-00T00:00:00Z
|
19th century | Any date in range 1801-1900 with precision 7 is interpreted as 19th century. This follows strict historical definition of century as explained in Wikipedia article. This might be counterintuitive to some, especially since it does not overlap with definition of decades. Also in some languages people do not use term like 19th century, but something equivalent to eighteen hundreds (1800s). |
| 6 | millennium | +1500-00-00T00:00:00Z
|
Second millennium | Any date in range 1001-2000 with precision 6 is interpreted as second millennium. As with centuries it might be counterintuitive to some. |
| 4 | hundred thousand years | -2500000-01-01T00:00:00Z
|
2,500,000 years BCE | Example from 2,500th millennium BC (Q3273066) item. |
| 3 | million years | -13798000000-01-01T00:00:00Z
|
13,798 million years BCE | Example from inflation (Q273508) item. |
| 0 | billion years | -5000000000-00-00T00:00:00Z
|
5 billion years BCE | Example from earth formation (Q3748186) item. |
Hours, minutes and seconds
[edit]Precisions higher than 11 (day) are not supported as of 2021. These would be:
| precision | timestamp string | meaning | |
|---|---|---|---|
| 14 | second | +2024-11-29T20:21:22Z
|
today at 20:21:22 |
| 13 | minute | +2024-11-29T20:21:00Z
|
today at 8:21 pm |
| 12 | hour | +2024-11-29T20:00:00Z
|
today at 8 pm |
There is a feature request to make this possible at phab:T57755.
Due to glitches in the api, a few values with such precision existed in Wikidata.
A workaround is to use the qualifier located in time zone (P421) together with the qualifier refine date (P4241) (described below) and values such as the items 11 PM (Q44529925), 23:00 (Q55812301) or 23:00:00 (Q95135875). Note the difference in precision of these items: hour, minute, second. A list of minute-precision items is at lists/time of the day.
There was also proposal for a dedicated qualifier (Property proposal/local time).
Properties opening time (P8626) and closing time (P8627) use time items as values as well. There were also some discussions to support one or the other string-based formats for such ranges.
Qualifiers
[edit]Qualifiers can be used to explain or customize dates that cannot be fully represented by the date model above. The precision of the date being qualified should have a precision that encompasses the range described by the qualifiers, or be set to "unknown value" (["snaktype"] = "somevalue"); you can choose an alternative value type by clicking the icon before the input box.
- earliest date (P1319) and/or latest date (P1326) - earliest and latest possible time that some event could have occurred.
- start time (P580) and/or end time (P582) - beginning and end of some period of time.
- sourcing circumstances (P1480) qualification of the accuracy of a statement. Allowed values: circa (Q5727902), near (Q21818619), presumably (Q18122778), disputed (Q18912752), etc.
- refine date (P4241) qualifier to narrow down the precision of a date. Allowed values:
- parts, like beginning of (Q40719727), middle of (Q40719748) and end of (Q40719766)
- halves, usually of a year, decade or century first half (Q40719687) and second half (Q40719707)
- quarters, usually of a century: first quarter (Q40690303), second quarter (Q40719649), third quarter (Q40719662) and fourth quarter (Q40719674)
- seasons, observed in northern and southern hemisphere
- winter (northern hemisphere) (Q40720553), spring (northern hemisphere) (Q40720559), summer (northern hemisphere) (Q40720564), autumn (northern hemisphere) (Q40720568)
- winter (southern hemisphere) (Q40720946), spring (southern hemisphere) (Q40720950), summer (southern hemisphere) (Q40720953), autumn (southern hemisphere) (Q40720956)
- Example dates and how to save them
Time qualifiers can also be used to provide more information about almost any statement. Those would be:
- start time (P580) and end time (P582) for describing period of time some statement was true
- point in time (P585) for describing point of time some statement was true
Properties
[edit]Full list of time properties can be found at Special:ListProperties/time.
Each person should have some properties related to lifespan:
| Information | How to store it | Comments |
|---|---|---|
| date of birth | date of birth (P569) | with precision "year" and qualifier determination method or standard (P459)=age for a given year mentioned in source (Q21042816): if a source mentions a person's age in a given year, this can be included this way. If only the birthday of a person is known without the year birthday (P3150) can be used. |
| date of death | date of death (P570) | with qualifier latest date (P1326): if a source mentions his widow in a given year, this can be stated with qualifier P1326. |
| date of baptism | date of baptism (P1636) | For many people we only know precise date of baptism, not birth. Often year of birth is stored with precise date of baptism. |
| date of burial or cremation | date of burial or cremation (P4602) | Similarly to date of baptism, sometimes only precise date of burial is known, which is than used to estimate month or year of death. |
| date of disappearance | date of disappearance (P746) | Date or point of time a missing person was seen or otherwise known to be alive for the last time. |
| alive | floruit (P1317) | Date when a person was known to be alive. Can help determine if a person born after 1901 is still alive or when a person without date of birth first came into the public eye. |
| (super-)centenarian | significant event (P793)=centenarian (Q2944360) significant event (P793)=supercentenarian (Q1200828) |
Person known to have reached 100/110 years. Can help determine if a person born before 1924 or 1914 is still alive. |
| work period or period when someone flourished (Latin: floruit or fl.) | Two ways to store it: | floruit (P1317) means date or period during which a person was known to have been alive or active, which is a little broader meaning than work period, as it might store dates when someone was alive but not active. In practice many people for whom we do not know the lifespan dates, we know only through their work, so those two properties would store the same information. Often floruit (P1317) stores information like 15th century, while work period (start) (P2031) and work period (end) (P2032) would store more precise date range. |
Time properties are also used to record significant dates related to artworks, books, buildings and other objects:
| Information | Property to store it | Applies to | How to use it |
|---|---|---|---|
| inception | inception (P571) | artwork book map music organization |
date or point in time when the organization/subject was founded/created |
| time of discovery | time of discovery or invention (P575) | artwork artifact astronomic objects inventions taxons |
date when the item was discovered |
| dissolved, abolished or demolished date | dissolved, abolished or demolished date (P576) | organization building |
date when an organization was dissolved/disappeared or a building demolished |
| publication date | publication date (P577) | book map music |
date or point in time a work is first published or released |
| first performance | date of first performance (P1191) | work music |
date a work was first debuted, performed or broadcasted |
| time of earliest written record | time of earliest written record (P1249) | ||
| discontinued date | discontinued date (P2669) | products | date that the availability of a product was discontinued |
| production date | production date (P2754) | date of production of a creative work, if different from the publication date | |
| date depicted | date depicted (P2913) | artwork book map |
date depicted in a work |
| public domain date | public domain date (P3893) | artworks books |
date the item enters into the public domain in a jurisdiction |
| date of official opening | date of official opening (P1619) | building event |
date an event, institution, or building opened |
| date of official closure | date of official closure (P3999) | building event |
date of official closure of a building or event |
| service entry | service entry (P729) | vehicle equipment |
date when a piece or class of equipment entered operational service |
| service retirement | service retirement (P730) | vehicle equipment |
date when a piece or class of equipment was retired from operational service |
| year of publication of scientific name for taxon | year of publication of scientific name for taxon (P574) | taxon | date when a scientific name was formally established. Together with taxon author (P405) used as qualifier of taxon name (P225). |
| UTC date of spacecraft launch | UTC date of spacecraft launch (P619) | spacecraft | |
| UTC date of spacecraft landing | UTC date of spacecraft landing (P620) | spacecraft | |
| time of object orbit decay | time of object orbit decay (P621) | spacecraft | |
| spacecraft docking/undocking date | spacecraft docking/undocking date (P622) | spacecraft | |
| periapsis date (DEPRECATED) | periapsis date (DEPRECATED) (P2285) | astronomical object | time for perihelion/perigee in each orbit for an astronomical object |
Recurring dates
[edit]For yearly recurring events there is day in year for periodic occurrence (P837), a special example is birthday (P3150). Help:Easter related dates helps with finding items for recurring days defined by their distance to Easter.
Property pairs for time periods
[edit]| from | to |
|---|---|
| inception (P571): time when an entity begins to exist; for date of official opening use P1619 | dissolved, abolished or demolished date (P576): point in time at which the subject (organisation, building) ceased to exist; see "date of official closure" (P3999) for closing a facility, "service retirement" (P730) for retiring equipment, "discontinued date" (P2669) for stopping a product |
| discontinued date (P2669): date that the availability of a product or service was discontinued; see also "dissolved, abolished or demolished" (P576) and "service retirement" (P730) for pieces or classes of equipment | |
| service retirement (P730): date or point in time on which a piece or class of equipment was retired from operational service ; use P2669 for end of a public service | |
| date of official closure (P3999): date of official closure of a building or event | |
| date of official opening (P1619): date or point in time an event, museum, theater etc. officially opened | date of official closure (P3999): date of official closure of a building or event |
| service entry (P729): date or point in time on which a piece or class of equipment entered operational service | service retirement (P730): date or point in time on which a piece or class of equipment was retired from operational service ; use P2669 for end of a public service |
| date of commercialization (P5204): date when a product was first commercialized | discontinued date (P2669): date that the availability of a product or service was discontinued; see also "dissolved, abolished or demolished" (P576) and "service retirement" (P730) for pieces or classes of equipment |
| start time (P580): time an entity begins to exist or a statement starts being valid | end time (P582): moment when an entity ceases to exist or a statement stops being valid |
| work period (start) (P2031): start of period during which a person or group flourished (fl. = "floruit") in their professional activity | work period (end) (P2032): end of period during which a person or group flourished (fl. = "floruit") in their professional activity |
| start period (P3415): initial period in which the statement is valid (including the period-value) | end period (P3416): last period in which the statement is still valid (including the period-value) |
| open period from (P3027): qualifier to P3025 (open days) for season when open days apply | open period to (P3028): qualifier to P3025 (open days) for season when open days apply |
| start of covered period (P7103): start of period covered by an archive set, a historical book, or a collection | end of covered period (P7104): end of period covered by an archive set, a historical book, or a collection |
| minimum date (property constraint) (P2310): qualifier to define a property constraint in combination with "property constraint" (P2302) | maximum date (property constraint) (P2311): qualifier to define a property constraint in combination with "property constraint" (P2302). Use "unknown value" for current date. |
| date of the first one (P7124): qualifier: when the first element of a quantity appeared/took place | date of the latest one (P7125): qualifier: when the latest element of a quantity appeared/took place |
| date of birth (P569): date on which the subject was born | date of death (P570): date on which the subject died |
| date of baptism (P1636): date when a person was baptized. For times when only baptism records were available, this can be a good substitute for date of birth. |
Interface
[edit]Entry of exact dates
[edit]When a date in 2024 is entered, e.g. 2024-11-29, the calendar model is set by default to proleptic Gregorian calendar (Q1985727).
For current dates, this works fine.
For earlier dates, the applicable calendar should be determined:
- The Gregorian calendar was first introduced in 1582 replacing the Julian calendar.
- The last countries to convert from the Julian to the Gregorian calendar did so in the 1920s. → w:Adoption of the Gregorian calendar.
Depending on the country and the source at hand, the applicable calendar has to be determined and entered.
- On manual entry, the software defaults to proleptic Gregorian calendar (Q1985727) from 1583.
- Dates before are considered by default as proleptic Julian calendar (Q1985786).
- In the advanced options, the calendar model can be changed.
If it can't be determined if the date is in one or the other calendar, that date should be entered in the default calendar with the qualifier sourcing circumstances (P1480) = unspecified calendar (Q18195782).
Some countries did use or still use other calendars. None of these are supported. Dates need to be converted to Julian or Gregorian.
Inexact dates
[edit]In quite a few cases the exact date of an event (like a date of birth) is not known. We have several approaches depending on how the source documents it.
End of automatically generated list. |
- Precision
The first approach is to change the precision. For example when the source says 1620s:
- Add a date claim
- Enter a year (for example 1625)
- Click "advanced adjustments"
- Change the precision to something suitable (for example a decade)
- Add the source
- Save the statement
- Qualifiers for earliest/latest
The first approach can be expanded if you know a before and/or after date. For example when the source says before 1625:
- Add the statement as above, but don't save it yet
- Add a qualifier latest date (P1326) and/or earliest date (P1319) with the date
- Save the statement
- Qualifier for circa
The second approach is suitable if the source says around a certain date or year. For example "around 1622":
- Add a date claim with a certain date
- Enter the year (for example 1622)
- Add qualifier sourcing circumstances (P1480) -> circa (Q5727902)
- Add the source
- Save the statement
Years BC
[edit]- Years BC should be entered as is.
- Sample: Year 458 BC on Q309637#P39 is entered as "458 BCE" and appears as "458 BCE".
- For RDF export (e.g. on Wikidata Query Service) the following applies: "The dates follow XSD 1.1 standard, i.e. 1 BCE is year 0."[1]. Year "0" is also exported as year 0, but only if it is Julian calendar, because non-Gregorian dates are passed through as is. Year 0 Gregorian is invalid in the database would not be exported. Year 2 BCE, as -1.
- Sample: Year 458 BC on https://www.wikidata.org/wiki/Special:EntityData/Q309637.rdf appears as "
<pq:P585 rdf:datatype="http://www.w3.org/2001/XMLSchema#dateTime">-0457-01-01T00:00:00Z</pq:P585>". The same is visible on the below SPARQL query.
SELECT *
{
VALUES ?item { wd:Q309637 }
?item p:P39 ?p1 . ?p1 pqv:P585 ?p3 . ?p3 ?p4 ?p5
}
LIMIT 100
- For RDF export (e.g. on Wikidata Query Service), dates BC (as any dates) are converted to Gregorian dates.
- Sample: 27 November 8 BCE appears as "-0007-11-25T00:00:00Z"
- For JSON export the format is inspired by XSD 1.0 and ISO 8601:1988. The year 0 is undefined, 1 BCE is exported as -0001, 2 BCE is exported as -0002, etc.
- Sample: Year 458 BC on https://www.wikidata.org/wiki/Special:EntityData/Q309637.json appears as
"{"time":"-0458-00-00T00:00:00Z","timezone":0,"before":0,"after":0,"precision":9,"calendarmodel":"http://www.wikidata.org/entity/Q1985786"}"
Filter dates inside sparql queries
[edit]Examples of syntax:
| Use case | Sparql |
|---|---|
| Any event that occurred between year X and year Y | SELECT ?item ?itemLabel ?time
WHERE
{
?item wdt:P585 ?time.
FILTER ( YEAR(?time) > 1450 && YEAR(?time) < 1454 ).
SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en" }
}
|
| Any event that occurred between a date X and a date Y | SELECT ?item ?itemLabel ?time
WHERE
{
?item wdt:P585 ?time.
FILTER ((?time > "1452-01-01"^^xsd:dateTime) && (?time < "1452-12-31"^^xsd:dateTime)).
SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en" }
}
|
| Any event that happened on a specific date | SELECT ?item ?itemLabel
WHERE
{
?item wdt:P585 "+1789-07-14T00:00:00Z"^^xsd:dateTime.
SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en" }
}
|
| People born in 1700 with day or month precision dates | SELECT ?item ?itemLabel ?time ?precision
WHERE
{
VALUES ?precision { 10 11 }#10 = month precision, 11 = day precision
?item p:P569/psv:P569 [wikibase:timePrecision ?precision; wikibase:timeValue ?time].
FILTER ( YEAR(?time) = 1700 ).
SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en" }
}
LIMIT 10
|
January 1 as date
[edit]Some dates from date of birth (P569):
| rank | January 1 | January 2 | January 3 |
|---|---|---|---|
| Normal rank | 21946 | 10842 | 10811 |
| Preferred rank | 284 | 151 | 153 |
| Deprecated rank | 1649 | 6 | 8 |
| ∑ | 23879 | 10999 | 10972 |
- as of 2022-02-02
- Query
A January 1 date of birth (P569) can occur for several reasons:
- (A) a person was born on January 1
- (B) a person's birth was registered as being on January 1
- (C) a person's exact date of birth is unknown, but was officially registered with the year and "January 1"
- (D) a database stores year precision dates with "January 1"
- (E) a conversion between some database and Wikidata led to the year of birth added as January 1 of that year.
Wikidata would generally include (A), (B), (C) with the appropriate reference and rank. (D) would generally be stored with deprecated rank or year precision. (E) should be corrected by changing the date precision to year.
Similar problems can be found with other dates, e.g. date of death (P570).
Known issues
[edit]See Phab:T87764 (Bugs related to time datatype (tracking))
- In 2015, the format for dates was changed. Julian dates entered before are likely to be off a few days.
- Some dates may have year precision, but have been entered as day precision
- The documentation indicates the time zone exists, but the only time zone that can be entered is an offset of 0 from w:universal time. Since it is impossible to capture the time zone of the source, most of the dates in Wikipedia are, strictly speaking, false.
- See Phab:T95553. The user interface accepts and presents dates with precision 7 (100 years) strangely, enticing editors to enter incorrect dates.