Class

• <DRM Variable>

Superclass

• <DRM Expression>

Subclass

• None.

Definition

An instance of this DRM class is used to connect an <DRM Interface Template> instance to a location within a tree of <DRM Expression> instances where outside control may be exerted.

For a <DRM Variable> instance contained within a <DRM Model> instance, evaluation is valid only for a specific instance of that <DRM Model> instance. The value is determined by a <DRM Expression> instance that is aggregated by the specific <DRM Geometry Model Instance> or <DRM Feature Model Instance> instance. This <DRM Expression> instance shall be associated to the same <DRM Interface Template> instance that is associated with the <DRM Variable> instance.

For a <DRM Variable> instance contained within a <DRM Environment Root> instance, the evaluation can only be performed within the context of values that shall be supplied by the consuming system.

The meaning field specifies the quantity represented by the given <DRM Variable> instance.

The value_unit field specifies the unit of measurement of the quantity represented by the given <DRM Variable> instance.

The value_scale field specifies the scale applicable to value_unit.

The value_type field specifies the value type of the given <DRM Variable> instance.

The description field specifies a meaningful explanation of the purpose of the given <DRM Variable> instance.

The runtime_label field is used for <DRM Variable> instances that consumers need to identify which represent run-time flags, provided so that appropriate values can be plugged in, which then affect any <DRM Control Link> instances driven by such a <DRM Variable> instance. If a <DRM Variable> instance does not need a runtime_label, the field is set to the empty string.

Class diagram

Figure 6.353 — DRM_Variable

Constraints

• Non crossing associations
• Non cyclic aggregations
• Publishable Object
• Variable meaning restrictions

Example(s)

• Consider a source database containing a <DRM Model> instance with some polygons that reference table driven textures. Such a polygon is defined as a <DRM Polygon> instance that has one reference to a <DRM Image> instance with multiple references to s and t values that are stored in a <DRM Data Table> instance. The index into this table is decided at run-time. Each <DRM Polygon> instance containing a table-driven texture has an identifier that is used, along with the index, at run-time.

  In the DRM, a <DRM Polygon> instance uses a <DRM Property Table Reference> instance to index into the <DRM Data Table> instance containing the different s and t values. Attached to the <DRM Property Table Reference> instance is a <DRM Property Table Reference Control Link> instance. The <DRM Variable> instance attached to this <DRM Property Table Reference Control Link> instance is ultimately associated to the <DRM Interface Template> instance on the <DRM Model> instance. The original identifier on the <DRM Polygon> instance shall reside on the <DRM Variable> instance rather than the <DRM Polygon> instance, since the <DRM Variable> instance controls the s and t values.

• The following is another example of how a runtime_label on a <DRM Variable> would be used. On moving models there might be polygons that have infrared values attached. Consider a tank <DRM Model> in such a database.

  In the DRM, the infrared values are stored in <DRM Property Table> instances. The <DRM Polygon> instances of the tank reference these elements through a <DRM Property Table Reference> instance. A <DRM Property Table Reference Control Link> instance is used for those <DRM Polygon> instances that have heat producing capability (for instance, the gun barrel), so that the index into the infrared table can be changed to other values as the gun is used and heats up. More than one <DRM Polygon> instance will contain the same ID. The consumer shall be able to identify the <DRM Polygon> instances (through the <DRM Control Link> and <DRM Interface Template> instances) by this ID so that he can switch these <DRM Polygon> instances to be heat producing.