Dates: dealing with calendars

calendar date Gregorian calendar Julian calendar AD and BC dates phrase-level encoding
date calendar

Encoding of old-style dates and dates expressed in the Julian calendar

In projects dealing with materials from the early 18th century or before, or with materials that use other dating systems (e.g. the Chinese or Jewish calendar), it may be useful to encode dates in a way that makes explicit the calendar being used. This will allow dates to be converted into dates in other calendars, which in turn would make it possible to create timelines that accurately represent events from different calendars, or to meaningfully search documents using different calendars. In effect, encoding the calendar for every date allows you to establish the absolute date of an event, as well as the date in any particular calendar.

To support these uses, the TEI provides the calendar attribute, whose value is the name of the calendar system within which the date is expressed. The TEI Guidelines suggest some possible values, including Julian, Islamic, and Revolutionary (i.e. French Revolution). These values are included in P5 schemas, but not in the P4 or P5 DTDs. In either case, we advise that if you are going to use the calendar attribute you choose the values you will permit, and include them as a value list within your schema or DTD. It may also be advisable to include a value indicating that the calendar is unknown, for instance if you are dealing with texts that fall within the transition period between Julian and Gregorian calendars.

It is expected that the value attribute (P4) or when attribute (P5) contains dates expressed in the Gregorian (i.e. modern Western) calendar.

Examples

Example 1 (P4)

<date value="2003-11-08" calendar="Hebrew">Heshvan 14, 5764</date>

Note that after midnight the Gregorian date was 11-09.

Example 1 (P5)

<date when="2003-11-08" calendar="Hebrew">Heshvan 14, 5764</date>

Note that after midnight the Gregorian date was 11-09.