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Time Wish List

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Wish list

This is a place to add your own issues/desires for the OWL-Time deliverable. Please try to attach your name to it.

Non-Gregorian Calendar support

-- Contributed by Simon Cox 2015-02-10

OWL-Time uses XSD datatypes for temporal position. These are tied to the Gregorian Calendar, which has limited scope and expressivity. Other time-systems are used in many technical and cultural contexts, including different calendars (Hebrew, Islamic, Baha'i, dynastic systems), ordinal reference systems (geologic periods, archeological eras) and temporal coordinate systems (geochronometry, Unix-time, GPS Time). A recent paper accepted for publication in Semantic Web Journal describes an extension (or a replacement) for OWL-Time which supports additional temporal reference systems, but leaves the encoding of the current cases supported by OWL-Time untouched.

Temporal reference systems

-- Contributed by Simon Cox 2015-02-10

A model or ontology for temporal reference systems (clocks, calendars, coordinate systems, ordinal reference systems) would enable the encoding of TRS instances and their publication in support of non-Gregorian temporal position.

OGC WKT for CRS and non-Gregorian Calendar Support

-- Contributed by Chris Little 2015-05-14

OGC is starting a standards working group to standardise specification of 360 and 365 day calendars which are widely used in environmental modelling.

OGC is also working on a Best Practice document for Time. Currently, this proposes at least 4 distinct temporal regimes: 1. Events - ordered and partially ordered events, without a clock (e.g. geologic layers, king lists, tree rings) 2. Timescale - a fully ordered discrete finite set of ticks determined by a physical clock (e.g. astronomical years, astronomical days, pendulum swings, TAI International Atomic Time) 3. CRS - continuous interpolated and extrapolated timescale represented by a number line and normal real arithmetic (e.g. Unix time, Julian Days, mya) 4. Calendar - a set of algorithms to relate everyday days, months and years to a CRS or Timescale. There are other regimes such as accounting periods, or relativistic time built up on observers' clocks, and the issue of unambiguous notations.

Both work items have identified a number of holes and inconsistencies in a variety of existing standards for Gregorian time.

Further support for uncertain temporal expressions

-- Contributed by Karl Grossner 2015-08-11

OWL-Time does support some uncertain expressions by means of interval relations accounting for "before," "after," (sometime) "during," etc. It does not allow for approximate and vague expressions such as "circa 560 CE" or "sometime in the early 1920's." These could be covered in two ways:

1. by allowing a '~' operator to accompany any ISO-8601 expression

2. by allowing the hasBeginning and hasEnd elements to be specified by intervals as well as by instants

e.g. the object of a hasEnd property could be an interval having earliestEnd and latestEnd properties

A number of further OWL-Time extensions, such as adding an "uncertain" operator ('?') to '~', for an entire ISO-8601 expression or parts thereof, are proposed in the fairly recent US Library of Congress document, **"Extended Date/Time Format (EDTF) 1.0"**

Extended support for common temporal structures

-- Contributed by Matthias Müller 2015-08-13

ISO 8601 considers the following temporal structures: Instants, (e.g. "2014-01-01:T10:00"), Durations (e.g. "P1M"), Intervals (e.g. "2014-08-15T18:06Z/2014-08-15T20:20:20Z"), and a special structure for connected repeating intervals (e.g. "R12/2015-01/P1M", which represents a somewhat special case of a recurring interval).

Currently undefined structures are: - Regularly recurring intervals (which are not necessarily connected; e.g. opening hours), - Regularly recurring instants (e.g. an alarm clock set to 7am in the morning, on every day), - Irregularly repeating instants (i.e. sets of instants), and - Irregularly recurring intervals (i.e. sets of intervals, e.g. for attendance records, activity periods, ...).

(A comprehensive discussion can be found at here: A Conceptual Model and Text-based Notation for Temporal Geometry .

There is no common encoding standard for these structures and a vast range of applications-specific solutions exist.