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Published

April 21

vr.tr.april-21 · thing-q2525

Let an agent handle April 21 as a calendar date with weekday computation, observances attributed to their traditions and sourced events.

Thing Registry Cross-cutting context XCT.TME
Bundle → Layer → Finding → QuestionsClassifiersWhat it isWhy it existsDistinguishing featuresWhat robots and AI may and may not doMoral aspectsOwnersLinks to other meta-modelsIdentity and identifiersDirect propertiesRecognitionCapabilities and actionsHazards and failure modesStandards and interfacesContext of useSources

Bundle → Layer → Finding → Questions Filled

4 bundles · 8 layers · 8 findings · 16 questions

Date Calendar facts.

Weekday

Computation.

Weekday

Weekday.

  1. On which weekday does April 21 fall in this year? measurement
  2. Is it a leap year? boundary

Calendar

Julian or Gregorian.

Calendar

Calendar system.

  1. Is the Julian or Gregorian calendar meant? boundary
  2. What is the equivalent date in the other calendar? measurement
Observances Holidays.

Holiday

Public holiday.

Holiday

Holiday status.

  1. Is April 21 a public holiday or observance here? provenance
  2. Which tradition or law sets it? provenance

Attribution

Traditions.

Attribution

Attributed observances.

  1. Which countries or communities observe something on this date, according to them? provenance
  2. Is the observance attributed rather than assumed? boundary
History Past events.

Events

On this day.

Events

Historical events.

  1. Which notable events happened on April 21, according to reliable sources? provenance
  2. Are dates given in the same calendar? boundary

Anniversaries

Recurring.

Anniversaries

Anniversaries.

  1. Which anniversaries fall on this date this year? provenance
  2. Which are round numbers? measurement
Planning Scheduling.

Countdown

Days until.

Countdown

Countdown.

  1. How many days until the next April 21? measurement
  2. From which date? definition

Work

Working day.

Work

Working day.

  1. Is it a working day for this organisation? provenance
  2. Do deadlines move? boundary

Classifiers Filled

Family
Thing Registry
Category
Cross-cutting context
Entry kind
thing
Plane
XCT
Domain
XCT.TME

What it is Filled

April 21, day 111 (day 112 in leap years) of the year in the Gregorian calendar, with 254 days remaining in both common and leap years. Observances on this date vary by country and tradition.

Why it exists Filled

Let an agent handle April 21 as a calendar date with weekday computation, observances attributed to their traditions and sourced events.

Distinguishing features Filled

  • The twenty-first day of April
  • Weekday varies by year
  • Observances vary by place
  • Julian and Gregorian dates differ by 13 days in this era

What robots and AI may and may not do Filled

Must not

  • Report anniversaries for April 21 without a source.
  • Present one country's April 21 holiday as observed everywhere.
  • Convert historical April 21 dates between calendars without saying so.

Only with a human decision

  • Fixing a legal deadline that falls on an April 21 public holiday.

May

  • Compute day-of-year and weekday for April 21 in a given year.
  • List events and observances on April 21 by country with sources.

Moral aspects Filled

  • False on-this-day claims spread quickly and attach to real people and events.

Who is affected

  • Calendar users
  • People named in anniversaries

Owners Filled

Steward

Nobody owns a date; calendar and holiday authorities set observances.

Links to other meta-models Filled

parent

  • Q11187254 - registry parent class

related

  • April - month
  • April 20 - date
  • calendar date - category
  • ISO 8601 - notation

What else AI and robots need to interact with it Filled

Identity and identifiers required Filled

  • Vercy registry: vr.tr.april-21
  • Wikidata: Q2525 (https://www.wikidata.org/wiki/Q2525)
  • ISO 8601: --04-21 recurring date

Direct properties not applicable Not applicable

  • day of year: 111 or 112 day - common year, leap year where different
  • days remaining: 254 days

Plane XCT: no invented physical properties.

Recognition optional Filled

  • Written 21 April or April 21
  • ISO format --04-21
  • Observances vary by country and tradition
  • A date on calendars.

Capabilities and actions required Filled

  • compute its weekday in a given year
  • check local and international observances
  • find sourced historical events
  • schedule events

Hazards and failure modes required Filled

  • Assuming observances are universal
  • Unsourced on-this-day events
  • Mixing Julian and Gregorian dates

Standards and interfaces required Filled

  • ISO 8601
  • National public holiday laws

Context of use required Filled

  • A calendar date for scheduling, holidays and anniversaries.
  • the recurring calendar date
  • specific dated days in given years

Sources Filled

  1. Wikidata item Q2525: April 21 - identity and sense of the item
  2. Wikipedia: April 21 - general description of the item

Open questions

  • Should dated days be separate entries?
  • How should observances be linked?
  • How should events be sourced?

Machine files

Card as JSON Specification Card backlog vercy.card/1

Provenance

thing registry research (pass 2) · unreviewed

Built from: models/things/publications/thing-q2525/spec.json