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Important Notes on the DDBC Time Authority Database

Dating Conventions

The base format for dates in the DDBC Time Authority Database is the Julian Day Number (JDN) format. This is a continuous number representing the number of days (and fractions of days) since noon, 12pm, GMT on an arbitrary day in the distant past which predates all recorded history . Julian Day Numbers are not to be confused with dates in the Julian Calendar - see below. For more information on the Julian Day system, the entry at Wikipedia is a good place to start.

When converting between Julian Day Numbers and dates in the western calendar, certain choices between calendrical conventions must be made. The modern western calendar is the Gregorian calendar, and its use today is standardized and all-pervasive. This, however, is a recent phenomenon (Russia, for example, adopted the Gregorian calendar only in 1918, and Greece as late as 1923), and so determining dates in the 'western calendar' before the 20th century is fraught with difficulty.

For the services offered by DDBC which are supported by this database, we have chosen to adopt the following conventions:  all conversion between dates in western-style formats and Julian Day Numbers (and, therefore, to and from reckonings in Chinese calendrical systems) follows the proleptic Gregorian calendar (i.e. the modern Gregorian calendar projected back into history), and the astronomical year numbering system (designating the year before 1 CE as year 0, not 1 BCE). In view of the inherent difficulties resulting from the use of different calendars throughout history, a choice must be made, and we believe this choice is both the most rational and the one which will be increasingly standard in future scholarship. This view is supported by the ISO 8601 standard.

Correspondances between Chinese dates and western dates calculated in this fashion may, therefore, be at odds with those reckoned according to different standards. As an example, the founding of the Qin Dynasty (秦代) occurred on the 15th of November, -0220, reckoned according to the proleptic Gregorian calendar and represented in astronomical year numbers (as is the case in our web interface). However, if one elects to use, for example, the proleptic Julian calendar and the Christian AD/BC system (i.e., no year 0), the same day in history would be reckoned to be the 16th of November, 221 BC. Of course, many other reckonings are possible depending on which calendars are used and which conventions are followed.

This is an unavoidable eventuality, whatever system is chosen, but in the future we hope to offer the ability for users of our services to specify the conventions employed in the conversion process. We hope this will be useful in establishing cross-references with dates in other sources, especially where the assumptions and conventions used in these sources are known.

Dealing with prolepsis in the Chinese calendar

Prolepsis, in this context, is the use of a dating system to cover events which do not occur during its legitimate time-frame. In this way the proleptic Gregorian or proleptic Julian calendars can be used to refer to dates before the existence of these calendars themselves.

In the context of the Chinese calendar, this phenomenon is commonly manifest in two kinds of circumstances:

To be able to cope with this, our database contains records which cover, where appropriate, a range of dates before and/or after the actual historical period spanned by a given era, emperor or dynasty. A result of this is that the extents of these periods as reported by the database will be inaccurate in some cases.

We have therefore introduced into our database a status field, which allows us to record that the period covered by the record in question is merely hypothetical, or 'proleptic'. This is indicated by a 'P' in this field. In addition, a start_from field has been added to facilitate the recording of lunar months which straddle a change in status: such a lunar month is represented in the database by two records, where the latter has a start_from value indicating the day on which it becomes valid. Please note, however, that the research required to accurately and exhaustively populate these fields has yet to be completed, and as a result the beginning and ending dates reported by the database for particular reigns should not be taken as authoratative.

Current Limitations

The DDBC Time Authority Database is a work in progress. Over the coming years we will continue to expand, update and improve the quality and utility of the data. However, for now, the following limitations must be noted:

This date is the 1st of January, 4713 BC in the proleptic Julian calendar, and the 24th of November, -4713 in the proleptic Gregorian calendar. See below for more details.

Creative Commons License The DDBC Time Authority Database from Dharma Drum Buddhist College (法鼓佛教學院)
is licensed under a Creative Commons Attribution-Share Alike 2.5 Taiwan License.