Table 6

An abstract DRM class that specifies a collection of <DRM Feature> and/or <DRM Feature Hierarchy> instances, organized according to some organizing principle specific to the particular subclass of <DRM Aggregate Feature> being considered.

For most subclasses of <DRM Aggregate Feature>, each individual branch of the aggregation is explicitly identified by a distinct link object. The various subclasses provide different mechanisms for organizing <DRM Feature>s, which include:

· ALTERNATE_HIERARCHY:
Each branch is a <DRM Feature Hierarchy> with a different <DRM Hierarchy Data> instance, representing a different way of organizing the same underlying collection of <DRM Feature> instances.

· CLASSIFICATION:
Each branch is a <DRM Feature Hierarchy> with a different <DRM Classification Data> instance, representing a different thematic layer, or a different classification of <DRM Feature> instances (e.g., roads, railroads) within a single thematic layer.

· LEVEL_OF_DETAIL:
Each branch is a <DRM Feature Hierarchy> with a distinct (but possibly overlapping), <DRM Base Level of Detail Data> instance, representing an alternative that is to be used at a specified level of detail.

· OCT_TREE:
The <DRM Aggregate Feature> represents an oct_tree, where each branch is a <DRM Feature Hierarchy> representing an octant within the oct_tree, as identified by its <DRM Oct Tree Data> instance.

· PERIMETER:
Each branch is a <DRM Feature Hierarchy> that is located within a different cell of an irregular spatial index, as defined by its <DRM Perimeter Data> instance.

· QUAD_TREE:
The <DRM Aggregate Feature> represents a quad_tree, in which each branch is a <DRM Feature Hierarchy> representing an quadrant within the quad_tree, as identified by its <DRM Quad Tree Data> instance.

· SPATIAL_INDEX:
The <DRM Aggregate Feature> represents a regularly spaced spatial index grid, in which each branch is a <DRM Feature Hierarchy> instance representing a different cell within the spatial index.

· STATE:
The <DRM Aggregate Feature> represents something that can take on different state values for a specified EDCS Attribute Code (the state_tag, which shall have the "state-related" property). Each branch is a <DRM Feature Hierarchy> instance with a different <DRM State Data> instance, representing an alternative that shall used to represent the <DRM Aggregate Feature> when it takes on the specified state value.

· TIME:
The <DRM Aggregate Feature> represents something that has different representations for different time periods, so that each branch is a <DRM Feature Hierarchy> instance with a distinct (though possibly overlapping) <DRM Time Constraints Data> instance, representing an alternative that shall be used for the time period specified by its <DRM Time Constraints Data>.

· UNION:
Each branch is a <DRM Feature>, which may be either a <DRM Primitive Feature> or a <DRM Feature Hierarchy> instance. The reason for organizing them into separate components is only minimally specified.

Example(s)

· An airport could be represented as a <DRM Union Of Features> that includes <DRM Linear Feature>s for the runways; a <DRM Point Feature> for the control tower; and <DRM Area Feature>s for the terminal and parking lots.

· A forested area could be represented at two levels of detail using a <DRM Leve Of Detail Related Features> object, with two component <DRM Union Of Features> having different scale ranges, each containing a single <DRM Areal Feature>. The <DRM Areal Feature> to be used at smaller scales would be simpler than the <DRM Areal Feature> to be used at larger scales.

· In the previous example, a third component <DRM Union Of Features> could be added to be used at even larger scales, where the single <DRM Areal Feature> is replaced by a large number of <DRM Point Feature>s representing individual trees.

· A lake that varies in size significantly with the seasons could be represented as a <DRM Time Related Features> object, with two (or more) component <DRM Union Of Features> objects, each containing a single <DRM Areal Feature> representing the lake.

· A large collection of features might be organized using a <DRM Classification Related Features> object, with multiple component <DRM Union Of Features> objects, containing cultural, vegetation, and surface drainage features, respectively.

Inherited field elements

field_name	range	Field_Data_Type
none

Field elements

field_name	range	Field_Data_Type
unique_descendant¹		Boolean
strict_organizing_principle²		Boolean

Associated to (one-way) (inherited)

· none

Associated to (one-way)

· none

Associated by (one-way) (inherited)

· zero or one <DRM Hierarchy Summary Item>

Associated by (one-way)

· none

Associated with (two-way) (inherited)

· zero or more <DRM Feature>s

· zero or more <DRM Geometry Hierarchy>s

· zero or more <DRM Property Grid>s

Associated with (two-way)

· none

Composed of (two-way) (inherited)

· zero or more {ordered} <DRM Attribute Set Index>s

· zero or one <DRM Classification Data>

· zero or more <DRM Label>s

· zero or more <DRM Property Table>s

· zero or more <DRM Property Table Reference>s

· zero or more <DRM Property Value>s

· zero or one <DRM Reference Surface>

· zero or one <DRM Rendering Priority Level>

· zero or more <DRM Sound Instance>s

· zero or one <DRM Time Constraints Data>

Composed of (two-way)

· zero or more <DRM Colour>s

· zero or more <DRM Feature Topology Hierarchy>s

· zero or more (ordered) <DRM Image Mapping Function>s³

· zero or one <DRM Perimeter Data>

· zero or one <DRM Presentation Domain>⁴

· zero or more <DRM Property Description>s

· zero or one <DRM Spatial Domain>

Composed of (two-way metadata) (inherited)

· zero or one <DRM Access>

· zero or more <DRM Browse Media>s

· zero or one <DRM Citation>

· zero or more <DRM Cross Reference>s

· zero or one <DRM Data Quality>

· zero or one <DRM Description>

· zero or one <DRM Keywords>

· zero or one <DRM Point Of Contact>

Composed of (two-way metadata)

· none

Component of (inherited)

· zero or more <DRM Union Of Features>s

· zero or more <DRM Alternate Hierarchy Related Features>s through <DRM Hierarchy Data>s

· zero or more <DRM Classification Related Features>s through <DRM Classification Data>s

· zero or one <DRM Environment Root>

· zero or one <DRM Feature Model>

· zero or more <DRM Level Of Detail Related Features>s through <DRM Base Level Of Detail Data>s

· zero or more <DRM Oct Tree Related Features>s through <DRM Oct Tree Data>s

· zero or more <DRM Perimeter Related Features>s through <DRM Perimeter Data>s

· zero or more <DRM Quad Tree Related Features>s through <DRM Quad Tree Data>s

· zero or more <DRM Spatial Index Related Features>s through <DRM Spatial Index Data>s

· zero or more <DRM State Related Features>s through <DRM State Data>s

· zero or more <DRM Time Related Features>s through <DRM Time Constraints Data>s

Component of

· none

Constraints

· Colour mapping restrictions

· Image mapping functions and texture coordinates

· No attribute conflicts

· Non-crossing aggregations

· Non-crossing associations

· Non-cyclic aggregations

· Precedence of Attribute_Set_Index

Notes

¹ If true, for any object that exists 'below' this aggregation, each object will appear in only one 'branch' of this aggregation. If false, then objects may appear in multiple 'branches' of this aggregation.

² If true, each 'branch' strictly follows the rules of this aggregation. If false, then each 'branch' might bend the rules a bit. For example, if this is a spatial aggregation, than a value of true indicates that objects will not cross the spatial extents defined by this aggregation relationship, and a value of false indicates that objects might cross those bounds. For another example, if this is a time-based aggregation, then a value of true indicates that all branches will only contain data valid for the times specified for each branch, and a value of false indicates that the branches have the option of including data that falls outside of the specified time ranges for that branch.

³ Supports "attributes for derived objects." That is, these components are used only to specify texture mapping information for geometry that

is derived from the <DRM Aggregate Feature> by the consumer. These <DRM Image Mapping Function>s shall use <DRM Image Anchor> components to specify the mapping.

⁴ This is needed because in many cases, a <DRM Aggregate Feature> may be significant only for a particular domain, e.g. radar.

Class diagram