TopoComplexPropertyType, topoComplexProperty Topology complex

148 Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved. 14 GML schema — Temporal information and dynamic features

14.1 General concepts

14.1.1 Overview

The GML temporal schemas include components for describing temporal geometry and topology, temporal reference systems, and the temporal characteristics of geographic data. The model underlying the representation constitutes a profile of the conceptual schema described in ISO 19108. The underlying spatiotemporal model strives to accommodate both feature-level and attribute-level time stamping; basic support for tracking moving objects is also included. Time is measured on two types of scale: interval and ordinal. An interval scale offers a basis for measuring duration, an ordinal scale provides information only about relative position in time. EXAMPLE A stratigraphic sequence or the geological time scale are examples of ordinal scales. Two other ISO standards are relevant to describing temporal objects: ISO 8601 describes encodings for time instants and time periods, as text strings with particular structure and punctuation; ISOIEC 11404 provides a detailed description of time intervals as part of a general discussion of language independent datatypes. The temporal schemas cover two interrelated topics and provide basic schema components for representing temporal instants and periods, temporal topology, and reference systems; more specialized schema components defines components used for dynamic features. Instances of temporal geometric types are used as values for the temporal properties of geographic features. NOTE The main temporal schema document is identified by the following location-independent name using URN syntax: urn:x-ogc:specification:gml:schema-xsd:temporal:3.2.1 The temporal topology schema document is identified by the following location-independent name using URN syntax: urn:x-ogc:specification:gml:schema-xsd:temporalTopology:3.2.1 The schema document for temporal reference systems is identified by the following location-independent name using URN syntax: urn:x-ogc:specification:gml:schema-xsd:temporalReferenceSystems:3.2.1 The dynamic feature schema document for representing time-varying properties of geographic features is identified by the following location-independent name using URN syntax: urn:x-ogc:specification:gml:schema-xsd:dynamicFeature:3.2.1 All schema documents are listed in Annex C.

14.1.2 Relationship with ISO 19108

The temporal geometry and topology components of the GML schema specified in this clause provide a conformant, partial implementation of the ISO 19108 temporal schema. The relationship is discussed in detail in D.2.5. Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved. 149 The ISO 19108 geometry and topology types implemented in GML are specified in ISO 19108; some additional constraints are specified in ISO 19108 for these types, which are also constraints on the temporal geometry and topology components of the GML schema. In addition, GML specifies complementary temporal schema components as described in D.3.11.

14.2 Temporal schema

14.2.1 Abstract temporal objects 14.2.1.1 AbstractTimeObject gml:AbstractTimeObject implements ISO 19108 TM_Object see D.2.5.2 and ISO 19108:2002, 5.2.2 and acts as the head of a substitution group for all temporal primitives and complexes. It is declared as follows: element name=AbstractTimeObject type=gml:AbstractTimeObjectType abstract=true substitutionGroup=gml:AbstractGML A gml:AbstractTimeObject may be used in any position that a gml:AbstractGML is valid. Its content model is defined as follows: complexType name=AbstractTimeObjectType abstract=true complexContent extension base=gml:AbstractGMLType complexContent complexType NOTE The content model of gml:AbstractTimeObject is a vacuous extension of AbstractGMLType. Types derived from this have the standard GML object properties available: abstractMetadataProperty, description, descriptionReference, name.

14.2.1.2 AbstractTimePrimitive

gml:AbstractTimePrimitive implements ISO 19108 TM_Primitive see D.2.5.2 and ISO 19108:2002, 5.2.3 and acts as the head of a substitution group for geometric and topological temporal primitives. It is declared as follows: element name=AbstractTimePrimitive type=gml:AbstractTimePrimitiveType abstract=true substitutionGroup=gml:AbstractTimeObject A gml:AbstractTimePrimitive may be used in any position that a gml:AbstractTimeObject is valid. Its content model is defined as follows: complexType name=AbstractTimePrimitiveType abstract=true complexContent extension base=gml:AbstractTimeObjectType sequence element name=relatedTime type=gml:RelatedTimeType minOccurs=0 maxOccurs=unbounded sequence extension complexContent complexType This extends the model for generic temporal objects with properties indicating relationships between this temporal primitive and other temporal primitives. The definition of gml:RelatedTimeType is provided in 14.2.1.4.