IEC 62541-11 :2020 pdf download – OPC unified architecture – Part 11: Historical Access.
4.5 Changes in AddressSpace over time Clients use the browse Services of the View Service Set to navigate through the AddressSpace to discover the HistoricalNodes and their characteristics. These Services provide the most current information about the AddressSpace. It is possible and probable that the AddressSpace of a Server will change over time (i.e. TypeDefinitions can change; NodeIds can be modified, added or deleted). Server developers and administrators need to be aware that modifying the AddressSpace can impact a Client’s ability to access historical information. If the history for a HistoricalNode is still required, but the HistoricalNode is no longer historized, then the Object should be maintained in the AddressSpace, with the appropriate AccessLevel Attribute and Historizing Attribute settings (see IEC 62541 -3 for details on access levels). 5 Historical Information Model 5.1 HistoricalNodes 5.1.1 General The Historical Access model defines additional Properties that are applicable for both HistoricalDataNodes and HistoricalEventNodes. 5.1.2 Annotations Property The DataVariable or Object that has Annotation data will add the Annotations Property as shown in Table 2.
The Annotations Property shall be present on every HistoricalDataNode that supports modifications, deletions, or additions of Annotations weather or not Annotations currently exist. Annotation data is accessed using the standard HistoryRead functions. Annotations are modified, inserted or deleted using the standard HistoryUpdate functions and the UpdateStructuredDataDetails structure. The presence of the Annotations Property does not indicate the presence of Annotations on the HistoricalDataNode. A Server shall add the Annotations Property to a HistoricalDataNode only if it will also support Annotations on that HistoricalDataNode. See IEC 62541 -4 for adding Properties to Nodes. A Server shall remove all Annotation data if it removes the Annotations Property from an existing HistoricalDataNode. As with all HistoricalNodes, modifications, deletions or additions of Annotations will raise the appropriate Historical Audit Event with the corresponding NodeId. 5.2 HistoricalDataNodes 5.2.1 General The Historical Data model defines additional ObjectTypes and Objects. These descriptions also include required use cases for HistoricalDataNodes. 5.2.2 HistoricalDataConfigurationType The Historical Access Data model extends the standard type model by defining the HistoricalDataConfigurationType. This Object defines the general characteristics of a Node that defines the historical configuration of any HistoricalDataNode that is defined to contain history. It is formally defined in Table 3. All Instances of the HistoricalDataConfigurationType use the standard BrowseName as defined in Table 6
AggregateFunctions is an entry point to browse to all Aggregate capabilities supported by the Server for Historical Access. All HistoryAggregates supported by the Server should be able to be browsed starting from this Object. Aggregates are defined in IEC 62541 -1 3. The Stepped Variable specifies whether the historical data was collected in such a manner that it should be displayed as SlopedInterpolation (sloped line between points) or as SteppedInterpolation (vertically-connected horizontal lines between points) when raw data is examined. This Property also effects how some Aggregates are calculated. A value of True indicates the stepped interpolation mode. A value of False indicates SlopedInterpolation mode. The default value is False. The Definition Variable is a vendor-specific, human readable string that specifies how the value of this HistoricalDataNode is calculated. Definition is non-localized and will often contain an equation that can be parsed by certain Clients. Example: Definition::= “(TempA – 25) + TempB” The MaxTimeInterval Variable specifies the maximum interval between data points in the history repository regardless of their value change (see IEC 62541 -3 for definition of Duration). The MinTimeInterval Variable specifies the minimum interval between data points in the history repository regardless of their value change (see IEC 62541 -3 for definition of Duration).