Change of terminology and consequently of API

[estebanzimanyi]

Overview

Currently, MobilityDB uses the term duration to refer to the "temporal type", which can be 'Instant', 'InstantSet', 'Sequence', 'SequenceSet'. This is not in accordance with the equivalent functionality in PostGIS which provides the function GeometryType to determine the type of a geometry as text, such as 'POINT', 'LINESTRING', etc. This prevents the use of "duration" for the usual meaning, e.g., as defined by the Cambridge dictionary:

the length of time that something lasts. He planned a stay of two years’ duration.

For this reason, currently MobilityDB provides a function timespan which correspond to the duration in the dictionary sense described above. Examples of usage are as follows

select timespan('{[2000-01-01 08:00, 2000-01-01 08:20], [2000-01-01 08:30, 2000-01-01 08:40]}'::periodset);
-- 00:30:00
select timespan('{[1@2000-01-01 08:00, 5@2000-01-01 08:20], [5@2000-01-01 08:30, 1@2000-01-01 08:40]}'::tfloat);
-- 00:30:00

However, there are two possible interpretations of such a function depending on whether the time gaps are included or not in the calculation.

Proposed solution

The proposed solution would be as follows

• Use the function temporalType for obtaining the temporal type, which is one of 'Instant', 'InstantSet', 'Sequence', 'SequenceSet'.
• Use the function duration for obtaining the duration without taking time gaps into consideration
• Use the function timespan for obtaining the duration taking time gaps into consideration

The proposed change in API would then be as follows

select temporalType('{[1@2000-01-01 08:00, 5@2000-01-01 08:20], [5@2000-01-01 08:30, 1@2000-01-01 08:40]}'::tfloat);
-- 'SequenceSet'

select duration('{[2000-01-01 08:00, 2000-01-01 08:20], [2000-01-01 08:30, 2000-01-01 08:40]}'::periodset);
-- 00:30:00
select duration('{[1@2000-01-01 08:00, 5@2000-01-01 08:20], [5@2000-01-01 08:30, 1@2000-01-01 08:40]}'::tfloat);
-- 00:30:00

select timespan('{[2000-01-01 08:00, 2000-01-01 08:20], [2000-01-01 08:30, 2000-01-01 08:40]}'::periodset);
-- 00:40:00
select timespan('{[1@2000-01-01 08:00, 5@2000-01-01 08:20], [5@2000-01-01 08:30, 1@2000-01-01 08:40]}'::tfloat);
-- 00:40:00

[mschoema]

Solved in Pull Request #54