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The SEDRIS Data Representation Model
APPENDIX A - Classes Alternate Hierarchy Related Features |
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An instance of this DRM class is an aggregation of <Feature Hierarchy> instances, in which each component <Feature Hierarchy> is an alternate representation of the same environmental entity, and the corresponding <Hierarchy Data> instance indicates why that particular alternate representation was provided.
Consider a collection of <Feature> instances representing a specific spatial region, for which there is a requirement that the <Feature> instances shall be efficiently accessible both by location and by classification (such as ECC_ROAD, ECC_RIVER, ECC_VEGETATION).
To satisfy this requirement, the data provider has chosen to use an <Alternate Hierarchy Related Features> instance with two components, in which one component (in this example, a <Quad Tree Related Features> instance) organizes the <Feature> instances spatially, while a second component (a <Classification Related Features> instance) organizes the <Feature> instances by EDCS Classification Code (ECC).
This class allows a single collection of <Feature> instances to be hierarchically organized in two or more different ways. In one component, the <Feature> instances might be organized spatially, while in another component they might be organized by classification. Each branch of an instance of this class provides a different access path to the same objects, where each branch is organized to be efficient with respect to a different access pattern.
| SE_Boolean | unique_descendants; | (notes) |
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| SE_Boolean | strict_organizing_principle; | (notes) |
An association between two <Feature> instances indicates that they are alternate representations of the same environmental object.
An association between a <Geometry Hierarchy> instance and a <Feature> instance indicates that the <Geometry Hierarchy> and the <Feature> are alternate representations of the same environmental object.
An association between a <Property Grid> instance and a <Feature> instance indicates that the <Feature> and the <Property Grid> (or some specific cell data within that <Property Grid>) are alternate representations of the same environmental object. Each associated <Property Grid> will indicate which is the case.
This relationship exists to support "attributes for derived objects." That is, these components are used only to specify texture mapping information for geometry that is to be derived from the <Aggregate Feature> by the consumer. These <Image Mapping Function> instances shall use <Image Anchor> components to specify the mapping.
This is needed for cases in which an <Aggregate Feature> is significant only for a particular domain, such as radar.
If this value is SE_TRUE, each 'descendant' of this aggregation - that is, each <Feature> instance that exists in the component tree rooted at the given <Aggregate Feature> - shall be unique, in the sense that it shall appear in only one 'branch' of this aggregation. If unique_descendants is SE_FALSE, at least one <Feature> instance appears in more than one 'branch' of the aggregation.
If this value is SE_TRUE, each 'branch' of this aggregation strictly complies with the organizing principle for its particular subclass. If this value is SE_FALSE, at least one 'branch' does not strictly comply with the given organizing principle. See the organizing principle constraint for each specific subclass for details.
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