Accessing Device Attributes

The predefined device attributes for each type of predefined device are stored in the Predefined Attribute (PdAt) object class.

The objects in the Predefined Attribute (PdAt) object class identify the default values as well as other possible values for each attribute. The Customized Attribute (CuAt) object class contains only attributes for customized device instances that have been changed from their default values.

When a customized device instance is created by a Define method, its attributes assume the default values. As a result, no objects are added to the CuAt object class for the device. If an attribute for the device is changed from the default value by the Change method, an object to describe the attribute's current value is added to the CuAt object class for the attribute. If the attribute is subsequently changed back to the default value, the Change method deletes the CuAt object for the attribute.

Any device methods that need the current attribute values for a device must access both the PdAt and CuAt object classes. If an attribute appears in the CuAt object class, then the associated object identifies the current value. Otherwise, the default value from the PdAt attribute object identifies the current value.