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Welcome to the Temporal-Abstract-Spec wiki

Second cut at structuring resources to input into the Abstract Conceptual Model for Time OGC23-049

Minutes of the OGC Temporal Domain Working Group
We are also experimenting with using an OGC Slack channel #temporal-DWG
Existing standards

ISO19111

ISO8601

DIS34000
Restrictive profiles of existing standards
Other useful Documents
Stakeholders in temporal infrastructure

ISO established an Ad Hoc group on Time and has voted to publish a temporal Vocabualry DIS34000

OGC Naming Authority

BIPM

IERS

MISB Moving Imagery Standards Board Processing of moving imagery often needs high precision coordinated time
Examples of good and bad practice See MISB Motion Imagery Handbook, Chapter 6
Examples or catalogue of temporal systems See Wikipedia List of Calendars and Current Time Standards
Draft text

Quid est ergo tempus?

Si nemo ex me quaerat, scio.

Si quaerenti explicare velim, nescio.

Saint Augustine, Confessions, XI

What then is time?

If no one asks me, I know.

If I wish to explain to him who asks, I do not know.

Temporal Regimes

This conceptual model proposes four regimes:

Event Regime - No clocks, logic only
Clock Regime - Clocks, ticks, integer arithmetic only, no –ve times
Coordinate Regime - CRSs, number line to interpolate between ticks, real arithmetic, extrapolate before zero/datum/epoch
Calendar Regime - Calendars, abnormal arithmetic, earth sun and moon rotations, months, weeks

1. Event Regime

Set of EVENTS ordered in time (ta, tb, tc, … tn), that may be: Finite or Countably infinite (like the integers)

No clocks

Simple Logic Operators defined to determine if 2 times are: The same, or one earlier, the other later (maybe an earliest and latest times?)

2 times define Relation(ta,tb), ta<tb, but NOT duration (tb-ta)

Any 3 or 4 events could allow logic (Allen 1983) such as:

 tb is in (ta,tc), ta<tb<tc

 (ta,tc) overlaps (tb,td), ta<tb<tc<td, 

 (ta,td) contains (tb,tc ), ta<tb<tc<td, 

 (ta,tb) disjoint from (tc,td), ta<tb<tc<td,

No other times exist or can be interpolated

Similar to RCC8 spatial operators

Not sure about continuum. Probably OK. Operations are the distinguishing features.

Examples: Geology, Archaeology, Ice and sediment cores, King Lists and Genealogies

Could be multiple sets, each with own ordering, may or may not be relations between events across sets

ISO8601 notation 2014-10-07T10:00 is a BAD notation for this regime. Notation should just be labels E.g. “Jurassic”, “65My ago”, “Reign of Tiglathpileser III”, "1.562m from top of core" (?? not sure about ice cores? Tree rings are definitely Regime 2, clocks)

2. Clock Regime

“Clock” defined as any regularly repeating physical event that can be counted (or perhaps measured?)

Countably infinite set of ordered time INSTANTS.

Fixed precision, determined by interval between instants

No intermediate times can be calculated between ticks

Similar set of operations: Same, Earlier/later, Operations for Instants and Intervals

 tb is in (ta,tc), ta<tb<tc

 (ta,tc) overlaps (tb,td), ta<tb<tc<td, 

 (ta,td) contains (tb,tc), ta<tb<tc<td, 

 (ta,tb) disjoint from (tc,td), ta<tb<tc<td,

Can now calculate duration (tb-ta) as metric defined

Could be an earliest or latest, or an epoch (datum time)

Examples:

TAI International Atomic Time, which cannot be used to time events to femtosecond precision, or cannot be used to time events prior to Epoch!
Pendulum swings
Heart-beat
Vibration of a piezo-electric crystal
Rotation of earth around sun

Notation implying higher accuracy than ticks not appropriate. E.g. Julian days labelled 2014-10-07T10:00:00.0+01:00

3. Coordinate Regime

Precision defined with countably infinite set of ‘ticks’

Assume normal mathematical interpolation between ticks

Epoch defined, perhaps with practical earliest/latest times

Assume mathematical extrapolation before epoch or into the future: +/-

Logical Operations and calculations well defined

Other ‘UoM’ can be defined but must be totally ‘regular’ E.g: 1 hour = 60 mins, 1 day=24 hours, 1 year = 360 days E.g: milliseconds, kiloseconds

Examples: Unix milliseconds, Julian Days, Julian Years, etc

Epoch may be ill-defined (start of reign of Ashburnipal III) so CRS is relative, not absolute – see Regime 0.

Epoch should be defined in terms of TAI, UTC, etc

Regimes 1 & 2 blend

Think carefully about timestamp notation, such as ISO8601: 2014-10-07T11:00:00.0 actually implies LOCAL time, which could be solar! 2014-10-07T10:00:00.0Z implies UTC, and therefore leap seconds

Astronomers epoch is usually at midday, everyone else prefers midnight, of specified day

4. Calendar Regime

Anything requiring an algorithm beyond normal arithmetic

E.g: Years CE and BCE (AD & BC). There is no year 0BCE or 0CE, so ‘normal arithmetic’ gives unexpected results E.g. UTC Gregorian, Mayan, Jewish, etc

Should have an Epoch

May have earliest and latest defined times, or times when algorithm invalid

Usually approximates a CRS to astronomical events

Algorithmic rather than observed calendar

A CRS is not a Calendar, a Calendar is not a CRS!

Time Scales and Calendars

All defined timescales and calendars, as they are based on physical devices, have a temporal scope; That is, a time interval for which they are valid. Outside of the this interval, people may still choose to use that temporal reference system, but with indeterminate accuracy and precision, and no method of determining them.