Calendar

Definition

A Calendar is a temporal reference system used in a particular cultural or scholarly context.

Usage

A calendar will typically encompass a set of algorithms that enables clock counts to be converted into everyday dates and times related to the movement of astronomical bodies (day, month, year).

Examples

• The Gregorian calendar is widely used in the Western world.
• The Julian calendar was used throughout Europe until the 16th century, and is still used for computing key dates in some orthodox Christian communities.
• Lunisolar (e.g. Hebrew) and lunar (e.g. Islamic) calendars are currently in use in some communities, and many similar have been used historically.
• Ancient Chinese calendars as well as the French revolutionary calendar used 10-day weeks.

In scientific and technical applications, Julian date counts the number of days since the beginning of 4713 BCE, and Loran-C, Unix and GPS time are based on seconds counted from a specified origin in 1958, 1970 and 1980, respectively, with GPS time represented using a pair of numbers for week number plus seconds into week.

Archaeological and geological applications use chronometric scales based on years counted backwards from ‘the present’ (defined as 1950 for radiocarbon dating [rc-14]), or using named periods associated with specified correlation markers ([cr-05], [cr-14], [mf-13]).

Dynastic calendars (counting years within eras defined by the reign of a monarch or dynasty) were used in many cultures. In order to support these more general applications, the representation of temporal position and duration must be flexible, and annotated with the temporal reference system in use.

References

• Time Ontology in OWL, W3C Candidate Recommendation Draft 15 November 2022