AbstractTimeSlice Representing dynamic features

Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved. 171 substitutionGroup=gml:AbstractGML complexType name=AbstractTimeSliceType abstract=true complexContent extension base=gml:AbstractGMLType sequence element ref=gml:validTime element ref=gml:dataSource minOccurs=0 sequence extension complexContent complexType A timeslice encapsulates the time-varying properties of a dynamic feature  it shall be extended to represent a time stamped projection of a specific feature. The gml:dataSource property describes how the temporal data was acquired. A gml:AbstractTimeSlice instance is a GML object that encapsulates updates of the dynamic —or volatile— properties that reflect some change event; it thus includes only those feature properties that have actually changed due to some process. EXAMPLE 1 Suppose that ownership of a building changes and it is renamed. If no other building properties have changed, then the event will only include the updated name. gml:AbstractTimeSlice basically provides a facility for attribute-level time stamping, in contrast to the object- level time stamping of dynamic feature instances. The time slice can thus be viewed as event or process-oriented, whereas a snapshot is more state or structure- oriented. A timeslice has richer causality, whereas a snapshot merely portrays the status of the whole. EXAMPLE 2 A feature collection might have a life cycle represented by a sequence of snapshots, see Figure 3. Figure 3 — The life cycle of a feature collection At instant t 1 , feature A, feature B, and feature C are all members of the collection. However, at instant t 2 only feature A and feature C are members. Closer examination of the history of feature B will reveal its ephemeral nature e.g. a building is dismantled and reconstructed on a seasonal basis.

14.5.7 history

A generic sequence of events constitute a gml:history of an object. This property element is declared as follows: 172 Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved. element name=history type=gml:HistoryPropertyType complexType name=HistoryPropertyType