metadata associated with an item at a given instance in time
Note 1to entry: An Annotationis metadata that is associated with an item at a given instance in time.
values associated with the starting and ending time
Note 1to entry: BoundingValuesare the values that are associated with the starting and ending time of a ProcessingIntervalspecified when reading from the historian. BoundingValuesmay be required by Clientsto determine the starting and ending values when requesting raw dataover a time range. If a raw datavalue exists at the start or end point, it is considered the bounding value even though it is part of the data request. If no raw datavalue exists at the start or end point, then the Serverwill determine the boundary value, which may require data from a data point outside of the requested range. See 4.4for details on using BoundingValues.
Note 1to entry: A HistoricalNodeis a term used in this document to represent any Object, Variable, Propertyor Viewin the AddressSpacefor which a Clientmay read and/or update historical data or Events. The terms “HistoricalNode’shistory” or “history of a HistoricalNode” will refer to the time series data or Eventsstored for this HistoricalNode. The term HistoricalNoderefers to both HistoricalDataNodesand HistoricalEventNodes.
Note 1to entry: A HistoricalDataNoderepresents any Variable or Property in the AddressSpace for which a Clientmay read and/or update historical data. “HistoricalDataNode’s history” or “history of a HistoricalDataNode” refers to the time series data stored for this HistoricalNode. Examples of such data are:
- device data (like temperature sensors)
- calculated data
- status information (open/closed, moving)
- dynamically changing system data (like stock quotes)
- diagnostic data
The term HistoricalDataNodesis used when referencing aspects of the standard that apply to accessing historical data only.
- system Alarms
- operator action Events
- system triggers (such as new orders to be processed)
Note 1to entry: For some Servers, a lab data entry value is not a modified value, but if a user corrects a lab value, the original value would be considered a modified value, and would be returned during a request for modified values. Also manually inserting a value that was missed by a standard collection system may be considered a modified value. Unless specified otherwise, all historical Servicesoperate on the current, or most recent, value for the specified HistoricalDataNodeat the specified timestamp. Requests for modified valuesare used to access values that have been superseded, deleted or inserted. It is up to a system to determine what is considered a modified value. Whenever a Serverhas modified data available for an entry in the historical collection it shall set theExtraData bit in the StatusCode.
data that is stored within the historian for a HistoricalDataNode
Note 1to entry: The data may be all data collected for the DataValueor it may be some subset of the data depending on the historian and the storage rules invoked when the item’s values were saved.
bounds of a history request which define the time domain
Note 1to entry: For all requests, a value falling at the end time of the time domain is not included in the domain, so that requests made for successive, contiguous time domains will include every value in the historical collection exactly once.
interval of time covered by a particular request, or response
Note 1to entry: In general, if the start time is earlier than or the same as the end time, the time domain is considered to begin at the start time and end just before the end time; if the end time is earlier than the start time, the time domain still begins at the start time and ends just before the end time, with time "running backward" for the particular request and response. In both cases, any value which falls exactly at the end time of the TimeDomainis not included in the TimeDomain. See the examples in 4.4. BoundingValueseffect the time domain as described in 4.4.
All timestamps which can legally be represented in a UtcTime DataTypeare valid timestamps, and the Servermay not return an invalid argument result code due to the timestamp being outside of the range for which the Serverhas data. See OPC 10000-3for a description of the range and granularity of this DataType. Serversare expected to handle out-of-bounds timestamps gracefully, and return the proper StatusCodesto the Client.
structured data stored in a history collection where parts of the structure are used to uniquely identify the data within the data collection
Note 1to entry: Most historical data applications assume only one current value per timestamp. Therefore the timestamp of the data is considered the unique identifier for that value. Some data or meta data such as Annotationsmay permit multiple values to exist at a single timestamp. In such cases the Server would use one or more parameters of the Structured History Dataentry to uniquely identifiy each element within the history collection. Annotationsare examples of Structured History Data.