The parameter SelectedFields defines the selection of Event fields contained in the DataSet generated for an Event and sent through the DataSetWriter. The SimpleAttributeOperand DataType is defined in OPC 10000-4. The DataType of the selected Event field in the EventType defines the DataType of the DataSet field. Event fields can be null or the field value can be a StatusCode. The encoding of Event based DataSetMessages shall be able to handle these cases. ExtensionFields defined for the instance of the PublishedEventsType can be included in the SelectedFields by specifying the PublishedEventsType NodeId as typeId in the SimpleAttributeOperand and the BrowseName of the extension field in the browsePath of the SimpleAttributeOperand.
The index into the list of entries in the SelectedFields has an important role for Subscribers. It is used as handle to reference the Event field in DataSetMessages received by Subscribers. The index may change after configuration changes. Changes are indicated by the ConfigurationVersion and applications working with the index shall always check the ConfigurationVersion before using the index. If a change of the SelectedFields adds additional fields, the MinorVersion of the ConfigurationVersion shall be updated. If a change of the SelectedFields removes fields, the MajorVersion of the ConfigurationVersion shall be updated. The ConfigurationVersionDataType and the rules for setting the version are defined in 18.104.22.168.5.