4 Aggregate information model

4.1 General

OPC 10000-3 and OPC 10000-5 standards define the representation of Aggregate historical or buffered real time data in the OPC Unified Architecture. This includes the definition of Aggregates used in processed data retrieval and in historical retrieval. This definition includes both standard Reference types and Object types.

4.2 Aggregate Objects

4.2.1 General

4.2.1.1 Overview

OPC UA Servers can support several different functionalities and capabilities. The following standard Objects are used to expose these capabilities in a common fashion, and there are several standard defined concepts that can be extended by vendors.

4.2.1.2 AggregateConfigurationType

The AggregateConfigurationType defines the general characteristics of a Node that defines the Aggregate configuration of any Variable or Property. AggregateConfiguration Object represents the browse entry point for information on how the Server treats Aggregate specific functionality such as handling Uncertain data. It is formally defined in Table 2.

The TreatUncertainAsBad Variable indicates how the Server treats data returned with a StatusCode severity Uncertain with respect to Aggregate calculations. A value of True indicates the Server considers the severity equivalent to Bad, a value of False indicates the Server considers the severity equivalent to Good, unless the Aggregate definition says otherwise. The default value is True. Note that the value is still treated as Uncertain when the StatusCode for the result is calculated.

The PercentDataBad Variable indicates the minimum percentage of Bad data in a given interval required for the StatusCode for the given interval for processed data request to be set to Bad. (Uncertain is treated as defined above.) Refer to 5.4.3 for details on using this Variable when assigning StatusCodes. For details on which Aggregates use the PercentDataBad Variable, see the definition of each Aggregate. The default value is 100.

The PercentDataGood Variable indicates the minimum percentage of Good data in a given interval required for the StatusCode for the given interval for the processed data requests to be set to Good. Refer to 5.4.3 for details on using this Variable when assigning StatusCodes. For details on which Aggregates use the PercentDataGood Variable, see the definition of each Aggregate. The default value is 100.

The following calculations are used to detemine the StatusCode which will be used to calculate the value of the aggregate. Refer to 5.4.3 for details on using these Variables when assigning StatusCodes. The PercentDataGood and PercentDataBad shall follow the following relationship PercentDataGood ≥ (100 – PercentDataBad). If they are equal the result of the PercentDataGood calculation is used. If the values entered for PercentDataGood and PercentDataBad do not result in a valid calculation (e.g. Bad = 80; Good = 0) the result will have a StatusCode of Bad_AggregateInvalidInputs The StatusCode Bad_AggregateInvalidInputs will be returned if the value of PercentDataGood or PercentDataBad exceed 100.

The UseSlopedExtrapolation Variable indicates how the Server interpolates data when no boundary value exists (i.e. extrapolating into the future from the last known value). A value of False indicates that the Server will use a SteppedExtrapolation format, and hold the last known value constant. A value of True indicates the Server will project the value using UseSlopedExtrapolation mode. The default value is False. For SimpleBounds this value is ignored.

4.2.2 AggregateFunction Object

4.2.2.1 General

This Object is used as the browse entry point for information about the Aggregates supported by a Server. The content of this Object is already defined by its type definition. All Instances of the FolderType use the standard BrowseName of ‘AggregateFunctions’. The HasComponent Reference is used to relate a ServerCapabilities Object and/or any HistoryServerCapabilitiesType Object to an AggregateFunction Object. AggregateFunctions is formally defined in Table 3.

Each ServerCapabilities and HistoryServerCapabilitiesType Object shall reference an AggregateFunction Object. In addition, each HistoricalConfiguration Object belonging to a HistoricalDataNode may reference an AggregateFunction Object using the HasComponent Reference.

4.2.2.2 AggregateFunctionType

This ObjectType defines an Aggregate supported by a UA Server. This Object is formally defined in Table 4.

For the AggregateFunctionType, the Description Attribute (inherited from the Base NodeClass), is mandatory. The Description Attribute provides a localized description of the Aggregate.

Table 5 specifies the BrowseName and Description Attributes for the standard Aggregate Objects. The description is the localized “en” text. For other locales it shall be translated.

4.2.2.3 Interpolative Aggregate Object

The Interpolative Aggregate Object is an instance of AggregateFunctionType and represents the interpolative aggregate function defined in 5.4.3.4. See Table 8 for details.

4.2.2.4 Average Aggregate Object

The Average Aggregate Object is an instance of AggregateFunctionType and represents the average aggregate function defined in 5.4.3.5. See Table 7 for details.

4.2.2.5 TimeAverage Aggregate Object

The TimeAverage Aggregate Object is an instance of AggregateFunctionType and represents the time average aggregate function defined in 5.4.3.6. See Table 8 for details.

4.2.2.6 TimeAverage2 Aggregate Object

The TimeAverage2 Aggregate Object is an instance of AggregateFunctionType and represents the time average 2 aggregate function defined in 5.4.3.7. See Table 9 for details.

4.2.2.7 Total Aggregate Object

The Total Aggregate Object is an instance of AggregateFunctionType and represents the total aggregate function defined in 5.4.3.8. See Table 10 for details.

4.2.2.8 Total2 Aggregate Object

The Total2 Aggregate Object is an instance of AggregateFunctionType and represents the total 2 aggregate function defined in 5.4.3.9. See Table 11 for details.

4.2.2.9 Minimum Aggregate Object

The Minimum Aggregate Object is an instance of AggregateFunctionType and represents the minimum aggregate function defined in 5.4.3.10. See Table 12 for details.

4.2.2.10 Maximum Aggregate Object

The Maximum Aggregate Object is an instance of AggregateFunctionType and represents the maximum aggregate function defined in 5.4.3.11. See Table 13 for details.

4.2.2.11 MinimumActualTime Aggregate Object

The MinimumActualTime Aggregate Object is an instance of AggregateFunctionType and represents the minimum actual time aggregate function defined in 5.4.3.12. See Table 14 for details.

4.2.2.12 MaximumActualTime Aggregate Object

The MaximumActualTime Aggregate Object is an instance of AggregateFunctionType and represents the maximum actual time aggregate function defined in 5.4.3.13. See Table 15 for details.

4.2.2.13 Range Aggregate Object

The Range Aggregate Object is an instance of AggregateFunctionType and represents the range aggregate function defined in 5.4.3.14. See Table 16 for details.

4.2.2.14 Minimum2 Aggregate Object

The Minimum2 Aggregate Object is an instance of AggregateFunctionType and represents the minimum 2 aggregate function defined in 5.4.3.15. See Table 17 for details.

4.2.2.15 Maximum2 Aggregate Object

The Maximum2 Aggregate Object is an instance of AggregateFunctionType and represents the maximum 2 aggregate function defined in 5.4.3.16. See Table 18 for details.

4.2.2.16 MinimumActualTime2 Aggregate Object

The MinimumActualTime2 Aggregate Object is an instance of AggregateFunctionType and represents the minimum actual time 2 aggregate function defined in 5.4.3.17. See Table 19 for details.

4.2.2.17 MaximumActualTime2 Aggregate Object

The MaximumActualTime2 Aggregate Object is an instance of AggregateFunctionType and represents the maximum actual time 2 aggregate function defined in 5.4.3.18. See Table 20 for details.

4.2.2.18 Range2 Aggregate Object

The Range2 Aggregate Object is an instance of AggregateFunctionType and represents the range 2 aggregate function defined in 5.4.3.19. See Table 21 for details.

4.2.2.19 Count Aggregate Object

The Count Aggregate Object is an instance of AggregateFunctionType and represents the count aggregate function defined in 5.4.3.21. See Table 22 for details.

4.2.2.20 DurationInStateZero Aggregate Object

The DurationInStateZero Aggregate Object is an instance of AggregateFunctionType and represents the duration in state zero aggregate function defined in 5.4.3.22. See Table 23 for details.

4.2.2.21 DurationInStateNonZero Aggregate Object

The DurationInStateNonZero Aggregate Object is an instance of AggregateFunctionType and represents the duration in state non-zero aggregate function defined in 5.4.3.23. See Table 24 for details.

4.2.2.22 NumberOfTransitions Aggregate Object

The NumberOfTransitions Aggregate Object is an instance of AggregateFunctionType and represents the number of transitions aggregate function defined in 5.4.3.24. See Table 25 for details.

4.2.2.23 Start Aggregate Object

The Start Aggregate Object is an instance of AggregateFunctionType and represents the start aggregate function defined in 5.4.3.25. See Table 26 for details.

4.2.2.24 End Aggregate Object

The End Aggregate Object is an instance of AggregateFunctionType and represents the end aggregate function defined in 5.4.3.26. See Table 27 for details.

4.2.2.25 Delta Aggregate Object

The Delta Aggregate Object is an instance of AggregateFunctionType and represents the delta aggregate function defined in 5.4.3.27. See Table 28 for details.

4.2.2.26 StartBound Aggregate Object

The StartBound Aggregate Object is an instance of AggregateFunctionType and represents the start bound aggregate function defined in 5.4.3.28. See Table 29 for details.

4.2.2.27 EndBound Aggregate Object

The EndBound Aggregate Object is an instance of AggregateFunctionType and represents the end bound aggregate function defined in 5.4.3.29. See Table 30 for details.

4.2.2.28 DeltaBounds Aggregate Object

The DeltaBounds Aggregate Object is an instance of AggregateFunctionType and represents the delta bounds aggregate function defined in 5.4.3.30. See Table 31 for details.

4.2.2.29 DurationGood Aggregate Object

The DurationGood Aggregate Object is an instance of AggregateFunctionType and represents the duration good aggregate function defined in 5.4.3.31. See Table 32 for details.

4.2.2.30 DurationBad Aggregate Object

The DurationBad Aggregate Object is an instance of AggregateFunctionType and represents the duration bad aggregate function defined in 5.4.3.32. See Table 33 for details.

4.2.2.31 PercentGood Aggregate Object

The PercentGood Aggregate Object is an instance of AggregateFunctionType and represents the percent good aggregate function defined in 5.4.3.33. See Table 34 for details.

4.2.2.32 PercentBad Aggregate Object

The PercentBad Aggregate Object is an instance of AggregateFunctionType and represents the percent bad aggregate function defined in 5.4.3.34. See Table 35 for details.

4.2.2.33 WorstQuality Aggregate Object

The WorstQuality Aggregate Object is an instance of AggregateFunctionType and represents the worst quality aggregate function defined in 5.4.3.35. See Table 36 for details.

4.2.2.34 WorstQuality2 Aggregate Object

The WorstQuality2 Aggregate Object is an instance of AggregateFunctionType and represents the worst quality 2 aggregate function defined in 5.4.3.36. See Table 37 for details.

4.2.2.35 AnnotationCount Aggregate Object

The AnnotationCount Aggregate Object is an instance of AggregateFunctionType and represents the annotation count aggregate function defined in 5.4.3.20. See Table 38 for details.

4.2.2.36 StandardDeviationSample Aggregate Object

The StandardDeviationSample Aggregate Object is an instance of AggregateFunctionType and represents the standard deviation sample aggregate function defined in 5.4.3.37. See Table 39 for details.

4.2.2.37 VarianceSample Aggregate Object

The VarianceSample Aggregate Object is an instance of AggregateFunctionType and represents the variance sample aggregate function defined in 5.4.3.38. See Table 40 for details.

4.2.2.38 StandardDeviationPopulation Aggregate Object

The StandardDeviationPopulation Aggregate Object is an instance of AggregateFunctionType and represents the standard deviation population aggregate function defined in 5.4.3.39. See Table 41 for details.

4.2.2.39 VariancePopulation Aggregate Object

The VariancePopulation Aggregate Object is an instance of AggregateFunctionType and represents the variance population aggregate function defined in 5.4.3.40. See Table 42 for details.

4.3 MonitoredItem AggregateFilter

4.3.1 MonitoredItem AggregateFilter Defaults

The default values used for MonitoredItem Aggregates are the same as those used for historical Aggregates. They are defined in 4.2.1.2. For additional information on MonitoredItem AggregateFilter see OPC 10000-4.

4.3.2 MonitoredItem Aggregates and Bounding Values

When calculating MonitoredItem Aggregates that require the use of Bounding Values, the bounds may not be known. The calculation is done in the same manner as a historical read with the Partial Bit set. The historian may wait some amount of time (normally no more than one processing interval) before calculating the interval to allow for any latency in data collection and reduce the use of the Partial Bit.

A historical read done after data collection and the data from the MonitoredItem over the same interval may not be the same.

4.4 Exposing Supported Functions and Capabilities

Figure 1 outlines a possible representation of Aggregate information in the AddressSpace. In this example, although the Server at the highest level may support Aggregate functionality for Interpolative, Total, Average, and others, DataVariable X only supports Interpolative, Total and Average, while DataVariable Y supports Average, a vendor defined Aggregate and other (unstated) Aggregates.