The SEDRIS Data Representation Model
APPENDIX A - Classes
Primitive Summary Item

Class Name: Primitive Summary Item

Superclass - <Base Summary Item>

Subclasses

This DRM class is concrete and has no subclasses.

Definition

An instance of this DRM class specifies a common pattern of primitive objects that appear in the scope being summarized, which may be either a <Model> instance or an <Environment Root> instance. A <Primitive Summary Item> instance represents one or more instances of the class specified by its drm_class field that conform to the specified pattern.

A <Primitive Summary Item> instance may represent only instances of <Primitive Geometry>, the <Primitive Feature>, and the classes that may appear in their component trees. <Primitive Summary Item> instances are combined to form a hierarchy mirroring that of the primitive instances that they represent such that the summary is a compressed form of the actual hierarchy.

Since a <Primitive Summary Item> instance may represent many instances of the primitive that it summarizes, it has a multiplicity field, indicating how many instances of the pattern it represents. Note that all instances represented by a <Primitive Summary Item> instance shall conform exactly to that pattern, up to the point where the summary's pattern ceases to provide specifics.

Primary Page in DRM Diagram:

Secondary Pages in DRM Diagram:

Example

  1. Summary of a common <Polygon> instance structure pattern within a <Model> instance.

    In this case, the pattern indicates that a data consumer can expect to see triangles. Other patterns can be present. As depicted in Figure 6.40, the <Model> instance contains not only triangles, but other types of <Polygon> instances, such as quadrilaterals and even five-sided <Polygon> instances. The <Primitive Summary Item> instances indicate common patterns and are not enumerating all the patterns that are present.

    Primitive Summary, Example 1

    Figure 40 — <DRM Primitive Summary Item> example

FAQs

Consider an <Environment Root> instance E with a <Primitive Summary Item> component, specifying a pattern of usage for instances of a given class. Does this mean that all instances of that class in the scope of E shall comply with the specified pattern?

No; it only indicates that the specified pattern is very common within the scope of E.

Consider an <Environment Root> instance E with a <Primitive Summary Item> component describing a texture-mapped triangular <Polygon> instance - that is, a <Polygon> instance with an <Image Mapping Function> component and three <Vertex> components. All that this means is that <Polygon> instances of that description are common in the scope of E.

Can the usage of a given class be simultaneously and unambiguously summarized by a <DRM Class Summary Item> instance and a <Primitive Summary Item> instance in the same scope?

Yes, because the <DRM Class Summary Item> class and the <Primitive Summary Item> class summarize different aspects of usage. The <DRM Class Summary Item> class summarizes the presence of instances of the specified class, while the <Primitive Summary Item> class represents common patterns of DRM objects in which instances of the specified class appear.

Constraints

Composed of (two-way)

Composed of (two-way metadata) (inherited)

Component of (two-way)

Inherited Field Elements

SE_DRM_Class drm_class; 2

Field Elements

SE_Integer_Unsigned multiplicity; 3

Notes

Composed of Notes


EDCS_Use_Summary_Item

If present, the list of <EDCS Use Summary Item> components of a <Base Summary Item> instance summarize EDCS usage by instances of the class specified by drm_class that occur somewhere in the scope being summarized.

Fields Notes

drm_class

The drm_class field indicates the DRM class of the DRM object(s) represented by the <Base Summary Item> instance.

multiplicity

The multiplicity field indicates the number of identical instances represented.


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Last updated: July 26, 2006 Copyright © 2006 SEDRIS