URI Space Representing Instants of Time in the Gregorian Calendar

This version:: http://placetime.com/2003/05/instant-gregorian-20030519
Latest version:: http://placetime.com/instant/gregorian/
Previous version:: http://placetime.com/2003/05/instant-gregorian-20030512
Author:: Ian Davis

Abstract

This is a specification of a URI space representing instants in time according to the Gregorian calendar.

Status

This URI space is EXPERIMENTAL and may be subject to change in the future. Please do not rely on the existence of any URIs in this space for production works.

Abstract
Status
The Gregorian calendar
URI syntax
Retrievability
Representations
Examples
Leap Seconds

The Gregorian calendar was devised under the direction of Pope Gregory XIII in order to correct inaccuracies that had crept into the existing Julian reckoning. It was adopted by various countries over a period of 400 years (see Dates of the Gregorian Reform).

The calendar is based on a 365-day year divided into twelve months of lengths 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30 and 31 days.

If a year is divisible by 4 and not by 100 or if it is divisble by 400 it is denoted a leap year and an extra day is added to the second month.

From time to time, a leap second may be added or subtracted to keep the calendar in step with astronomical time.

URI syntax

URIs in this space take the general form:

http://placetime.com/instant/gregorian/yyyy-mm-ddThh:nn:ssTZ

Where:

yyyy

Four digits (0,1,2,3,4,5,6,7,8,9) representing the year (0001 to 9999).

mm

Two digits representing the month of the year. (01 to 12)

dd

Two digits representing the day of the month. (01 to 28, 29, 30 or 31 depending on the month).

hh

Two digits representing the hour of the day. (01 to 23)

nn

Two digits representing the minute of the hour. (01 to 59)

ss

Two digits representing the second of the minute. (01 to 59, 60 or 61 depending on leap seconds)

TZ

A string that represents the timezone. This may be a literal 'Z' which denotes UTC time, or an offset in the form shh:nn where:

s: Either the character '+' which denotes a positive offset from UTC or '-' which denotes a negative offset
hh: Two digits representing the number of hours in the offset. (01 to 12)
nn: Two digits representing the number of minutes in the offset. (01 to 59)

The granularity of representation in this URI space is one second. In other words, there is exactly a one second interval between the instants represented by http://placetime.com/instant/gregorian/1992-07-12T22:01:04Z and http://placetime.com/instant/gregorian/1992-07-12T22:01:05Z. There is currently no way to represent instants with fractional seconds using this URI space. This document does not specify the duration of one second.

Note that there is currently no way to represent the same instant in different time-zones using this URI space. All times are specified in Coordinated Universal Time (UTC). Addition of time-zone information is under consideration.

Retrievability

All URIs in this space are retrievable via the HTTP protocol.

Content negotiation using the HTTP Accept: header is performed to determine the appropriate representation format.

Currently HTML and RDF representations are provided. These can be addressed individually by appending .html or .rdf to the URL used to retrieve the representation. For example an HTML representation of the URI

http://placetime.com/instant/gregorian/1970-06-15T19:31:00Z

may be obtained by issuing an HTTP GET on the following URL:

http://placetime.com/instant/gregorian/1970-06-15T19:31:00Z.html

and the corresponding RDF representation using this URL:

http://placetime.com/instant/gregorian/1970-06-15T19:31:00Z.rdf

Representations

The RDF representation of URIs in this space utilise the DAML-Time ontology. The URIs are instances of the DAML-Time Instant class.

Examples

http://placetime.com/instant/gregorian/2003-05-19T08:00:00Z: Eight o'clock in the morning, UTC, on the nineteenth day of the month of May in year two thousand and three of the Gregorian calendar.
http://placetime.com/instant/gregorian/1805-07-21T16:30:00Z: Thirty minutes past four o'clock in the afternoon, UTC, on the twenty-first day of the month of July in year eighteen hundred and five of the Gregorian calendar.
http://placetime.com/instant/gregorian/1969-07-20T16:17:43-04:00: Seventeen minutes and forty three seconds past four o'clock in the afternoon, four hours behind UTC, on the twentieth day of the month of July in year nineteen hundred and sixty nine of the Gregorian calendar.

Leap Seconds

Between 1972 and 2003 there have been 22 leap seconds added to the calendar due to tidal braking slowing the Earth's rotation. The decision to introduce a leap second is taken by the International Earth Rotation Service (IERS). Both positive and negative leap seconds can be introduced generally after the last day of the sixth or twelth months in a year, but occasionally after the last day of the third or ninth months. At the time of writing no negative leap seconds have been introduced.

The following URIs represent the start of the leap seconds introduced by the IERS (from ftp://maia.usno.navy.mil/ser7/leapsec.dat:

http://placetime.com/instant/gregorian/1971-12-31T23:59:60Z
http://placetime.com/instant/gregorian/1972-06-30T23:59:60Z
http://placetime.com/instant/gregorian/1972-12-31T23:59:60Z
http://placetime.com/instant/gregorian/1973-12-31T23:59:60Z
http://placetime.com/instant/gregorian/1974-12-31T23:59:60Z
http://placetime.com/instant/gregorian/1975-12-31T23:59:60Z
http://placetime.com/instant/gregorian/1976-12-31T23:59:60Z
http://placetime.com/instant/gregorian/1977-12-31T23:59:60Z
http://placetime.com/instant/gregorian/1978-12-31T23:59:60Z
http://placetime.com/instant/gregorian/1979-12-31T23:59:60Z
http://placetime.com/instant/gregorian/1980-12-31T23:59:60Z
http://placetime.com/instant/gregorian/1981-06-30T23:59:60Z
http://placetime.com/instant/gregorian/1982-06-30T23:59:60Z
http://placetime.com/instant/gregorian/1983-06-30T23:59:60Z
http://placetime.com/instant/gregorian/1985-06-30T23:59:60Z
http://placetime.com/instant/gregorian/1987-12-31T23:59:60Z
http://placetime.com/instant/gregorian/1989-12-31T23:59:60Z
http://placetime.com/instant/gregorian/1990-12-31T23:59:60Z
http://placetime.com/instant/gregorian/1992-06-30T23:59:60Z
http://placetime.com/instant/gregorian/1993-06-30T23:59:60Z
http://placetime.com/instant/gregorian/1994-06-30T23:59:60Z
http://placetime.com/instant/gregorian/1995-12-31T23:59:60Z
http://placetime.com/instant/gregorian/1997-06-30T23:59:60Z
http://placetime.com/instant/gregorian/1998-12-31T23:59:60Z