A user-configurable data group can be configured as either a "structure" or an "items" data group, reflecting the ScanCom device’s method of retrieval.
Structure data groups reference a fixed set of data group elements on the device, which are listed in the device template file file for UDC mapping only. If a data group element is added to a structure data group that is not defined in the structure on the device, an empty value will be returned, or an error will occur on a send.
Items data groups reference actual lists of data group element eElements, and can contain any elements. Adding or extending data groups requires the device documentation for structure definitions and/or data group element IDs.
Structure data groups may include a "freeze" attribute in the device template file. When true, any data retrievals will represent a frozen image of the data on the device, preventing retrieval of data that has been updated since the command was issued. In this way, the set of data returned is assured to be coherent at the given access time.
A third type of data group, "internal," is not user-configurable.
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