← Back to catalogue
Research draft

calendar date

vr.tr.calendar-date · XCT.TME

Let an agent handle dates with their calendar, precision, time zone dependence and format, and avoid the common errors of ambiguous or converted dates.

Thing Registry Cross-cutting context

Research draft, second pass

A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.

written by Claude from model knowledge without web access - no source was read, every claim is a lead to verify

Researched by: Claude

Purpose and description

Let an agent handle dates with their calendar, precision, time zone dependence and format, and avoid the common errors of ambiguous or converted dates.

A particular day identified within a calendar system, written as a combination of year, month and day or an equivalent reckoning.

What it is for: Identifying days, for records, deadlines, events and history.

It can be write and parse it, in a defined format; convert it between calendars; compute intervals between dates; record its precision, when only the year or month is known.

Distinguishing features

Belongs to a calendar system: Gregorian, Julian, Islamic, Hebrew and others

Has a precision: day, month, year, decade or circa

Depends on time zone when derived from an instant

Distinct from a time of day and from a time interval

What it looks like

Text such as 2026-09-11, 11/09/2026 or 11 September 2026; the same day is written differently across locales.

How it is recognised

Year, month and day components in some order

ISO 8601 format YYYY-MM-DD is unambiguous; slash formats are not

Date-of-birth, expiry and best-before dates are typed uses of the same concept

Related models

is part of - meaningful only within a calendar system

calendar

names - a date names one day

day

is confused with - a timestamp is an instant; a date is a whole day in a place

timestamp

has role - typed uses with their own rules

date of birth or expiry date

In practice

Families and kinds

by calendar: Gregorian, Julian, Islamic, Hebrew, Chinese, Persian and others

by precision: exact day, month, year, approximate

by role: date of birth, date of death, expiry, effective date

Identifiers

ISO 8601 YYYY-MM-DD standard representation

Julian Day Number integer day count calendar-independent count

Standards and regulation

ISO 8601 date and time representations

RFC 3339 for internet timestamps

Extended Date/Time Format (EDTF) for uncertain dates

Failure modes and hazards

Day-month order ambiguity, which silently swaps dates

Off-by-one day errors from time zone conversion

Julian and Gregorian confusion for historical dates

False precision when only the year is known

Also called

date of deathdate of birthbest before dateexpiration datebutsumetsudate of death of author(s)unknown vital datesdate of birth of authoraccession dateprefectural citizens' daysacred monthdate of prefacebicentennialGifaataaThe Glass of Reasonsesquicentennialanniversarysemiquincentennialanniversary of the foundingWikivoyage's 10th birthdaydeath anniversarysemicentennialcultural anniversaryjubileeCelebrating 700 years of the Swiss ConfederationYom HillulacentennialWikidata birthdayEnnichiVietnamese Women's Daycommemorative dayworld dayPatriotism MemorialUrsdiamond jubileesilver jubileeruby jubileeZentenariumsapphire jubileeplatinum jubilee

+769

Where this came from

wikidata · CC0 1.0

Source repository Registry entry point

Drafted structure

Bundle to layer to finding to question, as the second pass will find it: 4 bundles · 8 layers · 8 findings · 16 questions.

Calendar and precision Which calendar and how exact.

A date without its calendar and precision is ambiguous.

Calendar

The calendar system.

Calendar system

The calendar the date belongs to.

  1. Which calendar is this date expressed in? definition
  2. What is its equivalent in the Gregorian calendar? measurement

Precision

Day, month, year or approximate.

Precision level

How precisely the date is known.

  1. How precisely is this date known? measurement
  2. How should uncertainty be displayed? action
Format and parsing Writing and reading dates.

Most date errors come from formats.

Format

Written representation.

Format used

The format and locale.

  1. In which format is this date written? definition
  2. Is the order of day and month unambiguous? boundary

Parsing

Reading dates reliably.

Parsing rules

How the date is parsed.

  1. How should this text be parsed into a date? action
  2. What should happen when the format is ambiguous? action
Time zones Dates from instants.

The same instant falls on different dates in different places.

Derivation

Converting an instant to a date.

Zone used

The time zone used.

  1. In which time zone was this date derived? provenance
  2. Could the date differ in another relevant zone? boundary

Deadlines

Dates as deadlines.

Deadline interpretation

When a date deadline ends.

  1. When exactly does a deadline on this date expire? boundary
  2. Which time zone governs it? definition
Role and use What the date is for.

Typed dates carry rules: a date of birth is personal data, an expiry date has consequences.

Role

Birth, death, expiry, effective.

Date role

The role and its rules.

  1. What role does this date play in the record? definition
  2. What rules follow from that role? boundary

Protection

Personal data concerns.

Data protection

Whether it is personal data.

  1. Is this date personal data, such as a date of birth? boundary
  2. What limits apply to sharing it? action

What the second pass must settle

  • Should the registry require a calendar and precision for every date?
  • How should uncertain and approximate dates be recorded?
  • Which role types of date need their own entries?
Draft as JSON