ogc.gml.3.2.1.dynamicFeature.xsd Maven / Gradle / Ivy
dynamicFeature.xsd
See ISO/DIS 19136 15.6.
A number of types and relationships are defined to represent the time-varying properties of geographic features.
In a comprehensive treatment of spatiotemporal modeling, Langran (see Bibliography) distinguished three principal temporal entities: states, events, and evidence; the schema specified in the following Subclauses incorporates elements for each.
GML is an OGC Standard.
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Evidence is represented by a simple gml:dataSource or gml:dataSourceReference property that indicates the source of the temporal data. The remote link attributes of the gml:dataSource element have been deprecated along with its current type.
Evidence is represented by a simple gml:dataSource or gml:dataSourceReference property that indicates the source of the temporal data.
A convenience group. This allows an application schema developer to include dynamic properties in a content model in a standard fashion.
States are captured by time-stamped instances of a feature. The content model extends the standard gml:AbstractFeatureType with the gml:dynamicProperties model group.
Each time-stamped instance represents a 'snapshot' of a feature. The dynamic feature classes will normally be extended to suit particular applications. A dynamic feature bears either a time stamp or a history.
A gml:DynamicFeatureCollection is a feature collection that has a gml:validTime property (i.e. is a snapshot of the feature collection) or which has a gml:history property that contains one or more gml:AbstractTimeSlices each of which contain values of the time varying properties of the feature collection. Note that the gml:DynamicFeatureCollection may be one of the following:
1. A feature collection which consists of static feature members (members do not change in time) but which has properties of the collection object as a whole that do change in time .
2. A feature collection which consists of dynamic feature members (the members are gml:DynamicFeatures) but which also has properties of the collection as a whole that vary in time.
To describe an event — an action that occurs at an instant or over an interval of time — GML provides the gml:AbtractTimeSlice element. 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.
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.
A generic sequence of events constitute a gml:history of an object.
The gml:history element contains a set of elements in the substitution group headed by the abstract element gml:AbstractTimeSlice, representing the time-varying properties of interest. The history property of a dynamic feature associates a feature instance with a sequence of time slices (i.e. change events) that encapsulate the evolution of the feature.