Range parameters shall be substitutable for AbstractValue

236 Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved. Table 8 — Range parameters for coverage schemas Coverage Range parameter Definition in GML Temperature Distribution weather Temperature Would be derived from gml:MeasureOrNilReasonListType and made substitutable for gml:measure defined in 16.3.2. Soil type distribution agronomy Soil type Would be derived from gml:CategoryType and made substitutable for gml:Category. Weak reference to an enumeration of soil types. Multi-spectral optical image remote sensing Reflectance in each spectral band. Would be derived from gml:QuantityListType and made substitutable for gml:QuantityList. Distribution of West Nile Virus cases. epidemiology CaseCount Would be derived from gml:integerOrNilReasonList, and made substitutable for gml:CountList.

21.8.5 Coverage document

A coverage document is defined by a corresponding coverage schema. The root element of this document shall be a coverage defined in this schema or may be a feature collection as described in 9.9 whose members are coverages.

21.9 Schemas defining observations

21.9.1 Introduction

The following subclauses describe how to create an observation application schema. Observations are described in Clause 18. An observation application schema defines one or more types of observation in accordance with the following rules.

21.9.2 Import GML observation schema components

The application schema shall import the GML schema as described in 21.2.3. Any GML profile referenced from the application schema shall include at least the gml:Observation element and all schema components used by this element.

21.9.3 User-defined observation types

All observation types defined in the GML application schema shall be declared as global elements in the schema, i.e. they shall be child elements of the XML Schema schema element. The content model for such global elements shall derive by extension either directly or indirectly from gml:ObservationType. Authors of application schemas may create their own observation types if GML lacks the desired construct. To do this, authors shall ensure that the object elements of these observation types are in the substitution group either directly or indirectly of the corresponding GML object element: gml:Observation. NOTE 1 These elements are indirectly in the substitution group of gml:AbstractFeature and hence the condition of the feature model is satisfied. NOTE 2 This International Standard provides the concrete simple observation types gml:Observation, gml:DirectedObservation and gml:DirectedObservationAtDistance. Application observation types may derive from any of these as well. All rules specified in Clauses 7, 9 and 18 shall be followed. Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved. 237

21.9.4 Observation collections

All observation collections in the GML application schema shall be declared as global elements in the schema, i.e. they shall be child elements of the XML Schema schema element. An observation collection shall be a feature collection as described in 9.9 whose members are observations.

21.9.5 Observations are features

An observation defined in an application schema shall conform to the rules respecting GML features as described in Clause 9 and Clause 7. See also 21.3.4.

21.9.6 Observation collection document

Following the rules for GML documents see 21.1, an Observation Collection document may reference observations that are defined in any number of GML application schemas and these may define observations only, observation collections or any combination of the same.

21.10 Schemas defining dictionaries and definitions

21.10.1 Introduction

The following subclauses describe how to create an application schema for definitions. Definitions and dictionaries are described in Clause 15. One set of specialized definitions is built in to GML, for units of measure, and serves as an example of how to derive specialized definition components. An application schema for definitions defines one or more types of definition in accordance with the following rules.

21.10.2 Import GML dictionary schema components

The application schema shall import the GML schema as described in 21.2.3. Any GML profile referenced from the application schema shall include at least the gml:Definition element and all schema components used by this element.

21.10.3 User-defined definition types

All definitions in the application schema shall be declared as global elements in the schema, i.e. they shall be immediate child elements of the XML Schema schema element. The content model for such global elements shall derive either directly or indirectly from gml:DefinitionType. Authors of application schemas may create their own definition types if GML lacks the desired construct. To do this, authors shall ensure that the object elements of these definition types are in the substitution group either directly or indirectly of the corresponding GML object element: gml:Definition. All rules specified in Clauses 7 and 15 shall be followed.

21.10.4 User-defined dictionary types

A dictionary in the application schema shall be declared as a global element in the schema, that is it shall be a child element of the XML Schema schema element. The content model for such global elements shall derive either directly or indirectly from gml:DictionaryType.