History policies
The NiagaraNetwork's History Policies (HistoryNetworkExt) holds rules that are used when remote histories are “exported” into the local station. These are usually histories that are pushed from a remote station for archiving onto a supervisor station. Unlike imported histories, which let you define and adjust the capacity and full policy settings in each HistoryImportDescriptor, histories that are exported from one station into another station have no associated self-limiting parameters available at the exporting station. The capacity and full policy for each history is set at creation time, using the local history policies of the target station. These parameters affect the size of the history logs that are archived over the network. Usually the supervisor station is set to archive at a higher capacity than a remote station.
Figure 4-12 shows three different history policies under a NiagaraNetwork. These rules are all applied, in sequential order. Refer to the User Guide for more details about how the history policy rules are applied.
Figure 4-12 History policies under a Niagara Network
