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Operational historian refers to a database software application that logs or historizes time-based process data. Historian software is used to record trends and historical information about industrial processes for future reference. It captures plant management information about production status, performance monitoring, quality assurance, tracking and genealogy, and product delivery with enhanced data capture, data compression, and data presentation capabilities.
Operational historians are like enterprise historians but differ in that they are used by engineers on the plant floor rather than by business processes. They are typically cheaper, lighter in weight, and easier to use and reconfigure than enterprise historians. Having an operational historian enables "at the source" analysis of the historical data that is not typically possible with enterprise historians. Typically, these applications offer two layers of data access: through a dedicated SDK(Standard Development Kit)(sometimes in two different flavours: full administration API(Application Programming Interface) and high-speed read/write API), as well as user front-end tools (for instance, administration panels, engineering consoles or portal-like web clients).
Because these applications are designed to fulfil specific operation time requirements, their marketing materials often indicate that these are real-time database systems. However, since such performance measurements are often executed for atomic operations (especially write operations), not necessarily whole transactions, not all of the operational historians must be in fact real-time databases.
Usual challenges the operational historians must address are as follows:
- data collection from real-time external systems,
- storage and archiving of very large volumes of data,
- tag organisation (typically time series, where a single sample contains the information about the time stamp, the value and the sample quality),
- basic data limit monitoring (alarms) and user prompts (messages),
- performance of read and write operations.
As opposed to enterprise historians, the data access layer in the operational historian is designed to offer sophisticated data fetching modes without complex information analysis facilities. The following settings are typically available for data access operations:
- Data scope (single point, history based on time range, history based on sample count),
- Request modes (raw data, last-known value, aggregation, interpolation),
- Sampling (single point, all points without sampling, all points with interval sampling),
- Data omission (based on the sample quality, based on the sample value, based on the count).
Even though the operational historians are rarely relational database management systems, they often offer SQL-based interfaces to query the database. In most of such implementations, the dialect does not follow the SQL standard in order to provide syntax for specifying data access operations parameters.
- ABB Decathlon History
- Aspen Technology InfoPlus.21 
- Enea's Polyhedra Historian, a module of Polyhedra DBMS
- GE Intelligent Platforms Proficy Historian
- Honeywell Uniformance PHD
- Iconics Hyper Historian
- Inductive Automation SQL Bridge module of Ignition SCADA
- National Instruments Citadel, used in LabVIEW DSC and other products
- OSIsoft - PI System
- Schneider Electric InStep Software eDNA Real-Time Historian
- Schneider Electric Wonderware Historian
- Yokogawa Exaquantum Historian
- Jaaji Technologies inSis Infoview
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- Wonderware Historian - Example of naming the operational historian the real-time database
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