Table 56 defines the parameters for the Service.

Table 56 – HistoryRead Service Parameters







Common request parameters (see 7.28 for RequestHeader definition).


Extensible Parameter


The details define the types of history reads that can be performed. The HistoryReadDetails parameter type is an extensible parameter type formally defined in OPC 10000-11. The ExtensibleParameter type is defined in 7.12.



TimestampsTo Return

An enumeration that specifies the timestamps to be returned for each requested Variable Value Attribute. The TimestampsToReturn enumeration is defined in 7.35.

Specifying a TimestampsToReturn of NEITHER is not valid. A Server shall return a Bad_InvalidTimestampArgument StatusCode in this case.

OPC 10000-11 defines exceptions where this parameter shall be ignored.




A Boolean parameter with the following values:

TRUEpassed continuationPoints shall be reset to free resources in the Server.

FALSEpassed continuationPoints shall be used to get the next set of historical information.

A Client shall always use the continuation point returned by a HistoryRead response to free the resources for the continuation point in the Server. If the Client does not want to get the next set of historical information, HistoryRead shall be called with this parameter set to TRUE.

nodesToRead []


This parameter contains the list of items upon which the historical retrieval is to be performed. This structure is defined in-line with the following indented items.



If the HistoryReadDetails is RAW, PROCESSED, MODIFIED or ATTIME:

The nodeId of the Nodes whose historical values are to be read. The value returned shall always include a timestamp.

If the HistoryReadDetails is EVENTS:

The NodeId of the Node whose Event history is to be read.

If the Node does not support the requested access for historical values or historical Events the appropriate error response for the given Node shall be generated.



This parameter is used to identify a single element of an array, or a single range of indexes for arrays. If a range of elements is specified, the values are returned as a composite. The first element is identified by index 0 (zero). The NumericRange type is defined in 7.22.

This parameter is null if the value is not an array. However, if the value is an array, and this parameter is null, then all elements are to be included in the range.



A QualifiedName that specifies the data encoding to be returned for the Value to be read (see 7.24 for definition how to specify the data encoding).

This parameter only applies if the DataType of the Variable is a subtype of Structure. It is an error to specific this parameter if the DataType of the Variable is not a subtype of Structure.

The parameter is ignored when reading history of Events.



For each NodesToRead item this parameter specifies a continuation point returned from a previous HistoryRead call, allowing the Client to continue that read from the last value received.

The HistoryRead is used to select an ordered sequence of historical values or events. A continuation point marks a point in that ordered sequence, such that the Server returns the subset of the sequence that follows that point.

A null value indicates that this parameter is not used.

See 7.6 for a general description of continuation points.

This continuation point is described in more detail in OPC 10000-11.




Common response parameters (see 7.29 for ResponseHeader type).

results []


List of read results. The size and order of the list matches the size and order of the nodesToRead request parameter. This structure is defined in-line with the following indented items.



StatusCode for the NodesToRead item (see 7.34 for StatusCode definition).



This parameter is used only if the number of values to be returned is too large to be returned in a single response or if the timeout provided as hint by the Client is close to expiring and not all nodes have been processed.

When this parameter is not used, its value is null.

Servers shall support at least one continuation point per Session. Servers specify a max history continuation points per Session in the Server capabilities Object defined in OPC 10000-5. A continuation point shall remain active until the Client passes the continuation point to HistoryRead or the Session is closed. If the max continuation points have been reached the oldest continuation point shall be reset.


Extensible Parameter


The history data returned for the Node.

The HistoryData parameter type is an extensible parameter type formally defined in OPC 10000-11. It specifies the types of history data that can be returned. The ExtensibleParameter base type is defined in 7.12.

diagnosticInfos []

Diagnostic Info

List of diagnostic information. The size and order of the list matches the size and order of the nodesToRead request parameter. There is one entry in this list for each Node contained in the nodesToRead parameter. This list is empty if diagnostics information was not requested in the request header or if no diagnostic information was encountered in processing of the request.