Terms and definitions – OPC Unified Architecture

3.1 Terms and definitions

For the purposes of this document, the terms and definitions given in OPC 10000-1, OPC 10000-3, OPC 10000-4, OPC 10000-13 and the following apply.

3.1.1 Annotation

metadata associated with an item at a given instance in time

3.1.2 BoundingValues

values associated with the starting and ending time

3.1.3 Historian

application storing time series data and/or time series events

3.1.4 HistoricalNode

Object, Variable, Property or View in the AddressSpace where a Client can access historical data or Events

3.1.5 HistoricalDataNode

Variable or Property in the AddressSpace where a Client can access historical data

3.1.6 HistoricalEventNode

Object or View in the AddressSpace for which a Client can access historical Events

3.1.7 ModifiedValues

HistoricalDataNode ’ s value that has been changed (or manually inserted or deleted) after it was stored in the historian

Note 1

Note 1 to 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 ModifiedValues. Also manually inserting a value that was missed by a standard collection system can be considered a modified value. Unless specified otherwise, all historical Services operate on the current, or most recent, value for the specified HistoricalDataNode at the specified timestamp. Requests for ModifiedValues are used to access values that have been superseded, deleted or inserted.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 Server has modified data available for an entry in the historical collection it shall set the ExtraData bit in the StatusCode.

3.1.8 RawData

data that is stored within the historian for a HistoricalDataNode

3.1.9 StartTime/EndTime

bounds of a history request which define the time domain

3.1.10 TimeDomain

interval of time covered by a particular request, or response

Note 1

Note 1 to 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 TimeDomain is not included in the TimeDomain. See the examples in 4.6. BoundingValues effect the time domain as described in 4.6.

All timestamps which can legally be represented in a UtcTime DataType are valid timestamps, and the Server may not return an invalid argument result code due to the timestamp being outside of the range for which the Server has data. See OPC 10000-3 for a description of the range and granularity of this DataType. Servers are expected to handle out-of-bounds timestamps gracefully, and return the proper StatusCodes to the Client.

3.1.11 StructuredHistoryData

structured data stored in a history collection where parts of the structure are used to uniquely identify the data within the data collection