A Server supporting Historical Access provides Clients with transparent access to different historical data and/or historical Event sources (e.g. process historians, event historians, etc.).
The historical data or Events may be located in a proprietary data collection, database or a short term buffer within the memory. A Server supporting Historical Access will provide historical data and Events for all or a subset of the available Variables, Objects, Properties or Views within the Server AddressSpace.
Figure 1 illustrates how the AddressSpace of a UA Server might consist of a broad range of different historical data and/or historical Event sources.
Figure 1 – Possible OPC UA Server supporting Historical Access
The Server may be implemented as a standalone OPC UA Server that collects data from another OPC UA Server or another data source. The Client that references the OPC UA Server supporting Historical Access for historical data may be simple trending packages that just desire values over a given time frame or they may be complex reports that require data in multiple formats.