ANSI C Based OPC UA Client/Server/PubSub SDK
OpcUa_HistoryReadRequest Struct Reference

Asynchronously reads historical values or events of one or more nodes. More...

#include <opcua_types.h>

Data Fields

OpcUa_ExtensionObject HistoryReadDetails
 The details define the types of history reads that can be performed. More...
OpcUa_TimestampsToReturn TimestampsToReturn
 An enumeration that specifies the timestamps to be returned for each requested variable value attribute. More...
OpcUa_Boolean ReleaseContinuationPoints
 A Boolean parameter indicating whether to reset passed continuation points. More...
 contains the list of items upon which the historical retrieval is to be performed.

Detailed Description

Asynchronously reads historical values or events of one or more nodes.

For constructed attribute values whose elements are indexed, such as an array, this service allows Clients to read the entire set of indexed values as a composite, to read individual elements or to read ranges of elements of the composite. Servers may make historical values available to Clients using this service, although the historical values themselves are not visible in the address space.

The continuationPoint parameter in the HistoryRead is used to mark a point from which to continue the read if not all values could be returned in one response. The value is opaque for the Client and is only used to maintain the state information for the Server to continue from. A Server may use the timestamp of the last returned data item if the timestamp is unique. This can reduce the need in the Server to store state information for the continuation point.

In some cases it may take longer than the Client timeout hint to read the data for all nodes to read. Then the Server may return zero results with a continuation point for the affected nodes before the timeout expires. That allows the Server to resume the data acquisition on the next Client read call.

The documentation for this struct was generated from the following file: