TimeTopologyComplexPropertyType TimeNode TimeNodePropertyType Temporal topology objects .1 Overview

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14.3.2.8 TimeEdge

A time edge is a one-dimensional topology primitive. It is an open interval that starts and ends at a node. The edge may be realized as a geometry whose value is a time period. gml:TimeEdge implements ISO 19108 TM_Edge see D.2.5.6 and ISO 19108:2002, 5.2.4.4 and is declared as follows: element name=TimeEdge type=gml:TimeEdgeType substitutionGroup=gml:AbstractTimeTopologyPrimitive gml:TimeEdge may be used in any position that a gml:AbstractTimeTopologyPrimitive is valid. Its content model is defined as follows: complexType name=TimeEdgeType complexContent extension base=gml:AbstractTimeTopologyPrimitiveType sequence element name=start type=gml:TimeNodePropertyType element name=end type=gml:TimeNodePropertyType element name=extent type=gml:TimePeriodPropertyType minOccurs=0 sequence extension complexContent complexType

14.3.2.9 TimeEdgePropertyType

gml:TimeEdgePropertyType provides for associating a gml:TimeEdge with an object: complexType name=TimeEdgePropertyType sequence minOccurs=0 element ref=gml:TimeEdge sequence attributeGroup ref=gml:AssociationAttributeGroup attributeGroup ref=gml:OwnershipAttributeGroup complexType

14.4 Temporal reference systems

14.4.1 Overview

A value in the time domain is measured relative to a temporal reference system. Common types of reference system include calendars, ordinal temporal reference systems, and temporal coordinate systems time elapsed since some epoch. The primary temporal reference system for use with geographic information is the Gregorian Calendar and 24 hour local or Coordinated Universal Time UTC, but special applications may entail the use of alternative reference systems. The Julian day numbering system is a temporal coordinate system that has an origin earlier than any known calendar, at noon on 1 January 4713 BC in the Julian proleptic calendar, and is useful in transformations between dates in different calendars. In GML seven concrete elements are used to describe temporal reference systems: gml:TimeReferenceSystem, gml:TimeCoordinateSystem, gml:TimeCalendar, gml:TimeCalendarEra, gml:TimeClock, gml:TimeOrdinalReferenceSystem, and gml:TimeOrdinalEra. 162 Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved.

14.4.2 Basic temporal reference system, TimeReferenceSystem

A reference system is characterized in terms of its domain of validity: the spatial and temporal extent over which it is applicable. The basic GML element for temporal reference systems is gml:TimeReferenceSystem. Its content model extends gml:DefinitionType see 15.2.1 with one additional property, gml:domainOfValidity. It is implemented as follows: element name=TimeReferenceSystem type=gml:TimeReferenceSystemType substitutionGroup=gml:Definition gml:TimeReferenceSystem may be used in any position that a gml:Definition is valid. Its content model is defined as follows: complexType name=TimeReferenceSystemType complexContent extension base=gml:DefinitionType sequence element name=domainOfValidity type=string sequence extension complexContent complexType EXAMPLE This element might appear in an instance document as follows: gml:TimeReferenceSystem gml:id=JulianCalendar gml:description xlink:href=http:aa.usno.navy.mildatadocsJulianDate.html gml:nameJulian Calendargml:name gml:domainOfValidityWestern Europegml:domainOfValidity gml:TimeReferenceSystem

14.4.3 TimeCoordinateSystem

A temporal coordinate system shall be based on a continuous interval scale defined in terms of a single time interval. gml:TimeCoordinateSystem implements ISO 19108 TM_CoordinateSystem see D.2.5.9 and ISO 19108:2002, 5.3.3 with the exceptions specified below and is declared as follows: element name=TimeCoordinateSystem type=gml:TimeCoordinateSystemType substitutionGroup=gml:TimeReferenceSystem gml:TimeCoordinateSystem may be used in any position that a gml:TimeReferenceSystem is valid. Its content model is defined as follows: complexType name=TimeCoordinateSystemType complexContent extension base=gml:TimeReferenceSystemType sequence choice element name=originPosition type=gml:TimePositionType element name=origin type=gml:TimeInstantPropertyType choice element name=interval type=gml:TimeIntervalLengthType sequence extension complexContent complexType