Types of time value
Instants at different granularities
Spans, Intervals (Periods)
Open intervals
- Often use different types for valid and transaction times.
Notes:
“January 1998” is an instant with a granularity of 1 month.
“1998” is an instant with a granularity of a year.
Indeterminate instants, e.g. “1998” to a granularity of 1 month is a month sometime in 1998 but we don’t know when.
It is useful to record granularity separately, rather than just reduce everything down to intervals at the finest granularity.
“10 days” (granularity 1 day) is a span.
A period is a span with a defined start or end instant, which may be relative.
Relative, pure precedence “times” ? E.g. the farm was owned by Jean, then Pierre, then Jacques. Jean bought it in 1876 and Jacques sold it in 1893. Pierre’s ownership can be computed as the addition of these, so he will be returned as a possible owner for any query that specifies a time in the range 1876-1893.
Janet Bagg & Nick Ryan, (1997) Modelling historical change in southern Corsica: temporal GIS development using an extensible database system, Innovations in GIS 4, Zarine Kemp (Ed.), ISBN 0-7484-0657-3. They used datablades with Illustra (now Informix).. Note that this adds data types, it does not extend existing data-types (different terminology in their paper title than used in this presentation).