A Serversupporting Historical Access provides Clientswith transparent access to different historical data and/or historical Eventsources (e.g. process historians, event historians, etc.).

The historical data or Eventsmay be located in a proprietary data collection, database or a short term buffer within the memory. A Serversupporting Historical Access will provide historical data and Eventsfor all or a subset of the available Variables, Objects, Propertiesor Viewswithin the Server AddressSpace.

Figure 1illustrates how the AddressSpace of a UA Server might consist of a broad range of different historical data and/or historical Eventsources.

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Figure 1– Possible OPC UA Server supporting Historical Access

The Servermay be implemented as a standalone OPC UA Serverthat collects data from another OPC UA Serveror another data source. The Clientthat references the OPC UA Serversupporting 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.