About the Histories extension

Not all drivers have devices with a HistoryDeviceExt—notably, this exists only if the driver protocol (or device) provides local data logging. Currently, a Histories device extension exists under components NiagaraStation, ObixClient, R2ObixClient, and BacnetDevice (under a BacnetDevice, this extension is named “Trend Logs”).

“Database device” components in any of the RdbmsNetwork drivers (rdbSqlServer, rdbMySQL, etc.) also each have a Histories extension. See “Importing and exporting data using the RdbmsNetwork” in the Rdbms Driver Guide for related details.

Figure 45. Histories device extension (NiagaraStation)

A device’s Histories extension serves as the parent container for history descriptors—components that specify how history-type collections (log data) are imported or exported. By default, it also contains a Retry Trigger, see About the Retry Trigger.

The difference between a history import and history export are as follows:

Import

Any imported history appears in the local station as a Niagara history, where data is effectively “pulled” from a remote source device.
- For example, if a history import descriptor under Histories of a NiagaraStation device, the source is another Niagara history in that remote station.
- If a history import descriptor under Trend Logs of a BacnetDevice, the source is a BACnet Trend Log object residing in that BACnet device.
Export

Applies to a NiagaraStation (or “database device” under an RdbmsNetwork). An exported history is a Niagara history that exists in the local station, and is configured by a history export descriptor to “push” its data to a remote NiagaraStation (or RDBMS database). This adds it to the histories in that remote station (or to an RDBMS database).
Under a BacnetNetwork, the single “LocalDevice” component (that represents station data exported to BACnet) has a special view on its child Export Table component that permits exporting station histories as BACnet Trend Log objects. See the BACnet Guide section “Bacnet server configuration overview” for more details.

You create history import descriptors and export descriptors under the Histories extension of a device using separate views. For details, see About Histories extension views.