Time in GML
Geography is not only concerned with space and neither is GML. The temporal.xsd schema (see http://schemas.opengis.net/gml/3.1.1/base/temporal.xsd ) contains a set of useful definitions for time related objects and properties. The simplest of these is TimeInstant.
A TimeInstant is what it says - an instant in time. It has a single child (property) called timePosition. A TimeInstant is thus written:
<TimeInstant> <timePosition>1876-08-01</timePosition> </TimeInstant>Of course not all times are instants - some are TimePeriods. For these we can write:
<TimePeriod> <begin> <TimeInstant> <timePosition>1876-08-01</timePosition> </TimeInstant> </begin> <end> <TimeInstant> <timePosition>1876-08-02</timePosition> </TimeInstant> </end> </TimePeriod>Of course GML can provide a number of ways of expressing time durations and time lengths as well and can deal with non-ISO times and dates (need a Geological Calendar?) but that is beyond our scope for now.
