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The SEDRIS Data Representation Model
APPENDIX A - Classes DRM Class Summary Item |
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An instance of this DRM class is used as part of a summary of the content of a transmittal to indicate that at least one instance of the DRM class specified exists in that transmittal. <DRM Class Summary Item> instances are combined together to form a list of the classes that are present in a transmittal or part of a transmittal. Each such list has only one entry per class. However, it does not have to be a complete list of every class used, and it can include abstract classes.
Each <DRM Class Summary Item> instance can optionally have a list of <EDCS Use Summary Item> components giving the classifications that are attached to instances of the given class in the transmittal. This only may exist for those classes that can have classification information.
Each <DRM Class Summary Item> instance can also have a list of <SRF Summary> components giving the SRFs defined in the transmittal by instances of that class. This only may exist for those classes that contain SRF context information.
A summary of the classes used in an entire transmittal, as depicted in Figure 12
A summary of classes used in part of a transmittal.
Assume that the geometry portion of the given <Environment Root> instance has the layout depicted in Figure 13.
The geometry portion of the given <Environment Root> instance is therefore summarized as depicted in Figure 14.
This illustrates the possible use of a <DRM Class Summary Item> instance if we were to use a <Hierarchy Summary Item> instance to show only the top level hierarchy (for some reason).
The data producer may decide, for a number of reasons, that it would be useful to summarize the hierarchy down to a certain level only, but that it is also useful to show that there are aggregates such as <Union Of Primitive Geometry> instances below that level - i.e., showing that they exist, rather than showing their position in the hierarchy, is what is of value.
This isn't ambiguous because the two classes (<DRM Class Summary Item> and <Primitive Summary Item>) summarize different aspects of a transmittal. Therefore the same classes can (and will) quite legitimately be represented by both. So <Polygon> instances and <Vertex> instances can be described by <DRM Class Summary Item> instances, to summarize their presence in the transmittal, and as <Primitive Summary Item> instances, to show common patterns of DRM objects in which they are used.
The drm_class field indicates the DRM class of the DRM object(s) represented by the <Base Summary Item> instance.
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