Historical Data Access addresses the handling of historical time series data. The AddressSpace of HDA Servers contains Historical Nodes representing the history of Variables and Properties. HDA Clients deal with historical data by accessing these Nodes with the HistoryRead and HistoryUpdate Services. There are several types of Historian servers. Some key types supported by OPC UA are:
- Simple trend data servers, providing little other than simple raw data storage. (Data would typically be the types of data available from a Data Access server.
- Complex data compression and analysis servers, providing data compression as well as raw data storage. They are capable of providing summary data or data analysis functions, such as average values, minimums and maximums etc. They can support data updates and history of the updates. They can support storage of annotations along with the actual historical data storage.
Note – Historical Access is specified in OPC UA Part 11, Aggregates are specified in OPC UA Part 13.