Background information/Discussion:
It has been estimated that the number of  calendars in current use around
the world is about 40.

The most widely used seems to be the Gregorian -- or a variation, the Common
Era -- calendar.  I provided a brief history of the Gregorian and its
relationship to its predecessor, the Julian, so I won't rehash that
information.

Some other calendars bear noting in the context of DC Lib:

The Julian calendar: For Western agencies that create metadata for
historical documents, Julian dates continue to be of interest -- Western
documents prior to the 1580's (and depending on the country into the 1700's
or even as late as the 1920's [for Turkey]) would have borne a Julian date
(and precise conversion to Gregorian may require some historical knowledge
of the locale of the origin of the document -- Julian dates at times were
out of synch across national borders once the Gregorian scheme became
available). The Julian is still in use by several Orthodox churches but has
passed out of civil use.  Helpfully, contemporary Julian dates are very
close to Gregorian, e.g.,
March 2, 2002 Julian calendar = March 15, 2002 Gregorian.

The Hebrew calendar: The religious calendar of  Jews and the civil calendar
of Israel.  The general structure (CCYY-month-[24-hour]days, 7 days in a
week) of the Hebrew calendar resembles the Gregorian, but the terminal
points of years, months, weeks, days differ.  Lengths of months and years
are more variable, however, and leap years add an additional month, making
some years 12 months, others 13 months.  Days are always divided into 12
hours of darkness and 12 hours of daylight (thus the elapsed time of
individual hours varies over the course of a year) and are reckoned from
sunset to sunset.  The origin point (year 1) of the calendar is the
beginning of the world (3761 BC) (in Latin, "Anno Mundi" = year of the
world, and the abbreviation, "A.M." is often used in the West to denote a
Hebrew calendar year; e.g., 5762 A.M.).
A sample date: 2 Nisan 5762 (= March 15, 2002 Gregorian )

The Islamic calendar: The religious calendar of Muslims and the civil
calendar (observed in several slight variations) of a number of Islamic
countries. The general structure (CCYY-[12]month-days, 7 days in a week) of
the Islamic calendar resembles the Gregorian, but the terminal points of
years, months, weeks, days differ.  As a lunar calendar, the year is shorter
than the Gregorian, solar-based, year.  Days are reckoned sunset to sunset.
The origin point is the Hijira (i.e. Mohammed's emigration to Medina in 622
AD) (in Latin, Anno Hegirae = year of the Hijira, and the abbreviation,
"A.H." is often used in the West to denote a Hebrew calendar year; e.g.,1423
A.H. ).
A sample date: 1 Muharram 1423 (= March 15, 2002 Gregorian)

Other calendars such as the Indian calendar, Chinese calendar, etc. are also
in significant use.  Patterns of the various calendars follow or diverge
from the Gregorian CCYY-month-day approach to varying degrees.

Lastly: as might be expected calendars and time of day patterns and
notations are expressed in a meaningful way for employ the vernacular script
and writing direction (including bi-directional in some cases) appropriate
to the host culture.  Most of the major ones seem to have accepted, Western
equivalents, often using transliterated month names.

Analysis: non-Gregorian/CE dates:
-ISO 8601 & W3C-DTF make no provision for non-Gregorian dates (except by
conversion of non-Gregorian dates to Gregorian values)
-AACR2 1.4F1 provides for the following instruction for non-Gregorian dates:
"If the date found in the item is not of the Gregorian or Julian calendar,
give the date as found and follow it with the years) of the Gregorian or
Julian calendar."
-DCMI Period's default encoding is W3C-DTF so it does not really provide
ready support for non-Gregorian dates though it is possible to explicitedly
indicate a scheme so in theory one could use DCMI Period.
-MARC 21 currently only supports encoding Gregorian dates, though obviously
non-Gregorian dates could be recorded as text in selected fields.
Modifications to MARC 21 to allow for recording non-Gregorian dates in
encoded form have been discussed (see
http://www.loc.gov/marc/marbi/dp/dp117.html)

Recommendations/options:
RG: Non-Gregorian dates: I don't know how important this is; maybe just use
free-text? We usually convert them in MARC to Gregorian.
EC: Do we have a large user base for DC-Lib right now that we think likely
to want to use non-Gregorian dates? My guess is no, but maybe others no
better.  Overall conversion to Gregorian (best: W3C-DTF or ISO8601) or
free-text seem like the best options available to us at the moment. It's
possible that we could provide limited guidance for free text values for
some schemes (e.g., recommending that non-Gregorian calendar years in the
Islamic calendar be recorded as "[Western abbreviation] [CCYY]" e.g., A.H.
1423), but I'm not sure this would be useful to a significant degree.
Long-term, we need to have users who need non-Gregorian dates either
identify encoding schemes that DCMI can recognize, or a new encoding scheme
needs to be developed.


Eric Childress
Consulting Product Manager
OCLC Metadata Services Division
OCLC Online Computer Library Center, Inc.
6565 Frantz Rd., Dublin, OH 43017 USA
US: (800) 848-5878 or (614) 764-6000
Fax: (614) 718-7361 email: [log in to unmask]

2) Non-Gregorian dates: I don't know how important this is; maybe just use
free-text? We usually convert them in MARC to Gregorian.