Historian

In the previous sections, we saw how data acquisition in SCADA systems starts from the controllers (the PLCs or the DCSs) or RTUs gathering measurements from sensors and equipment through industrial protocols. The digital representations of these measures are usually called tags or datapoints. Each of these represents a single input or output signal that is monitored or controlled by the system. They usually appear as value-timestamp pairs. After generation, the data can also be sent to other monitoring servers for analysis by humans or to the MES system for planning and maintenance. At the same time, data often feeds a specialized database for storing and managing times series. This specialized database is called Historian, or data Historian. Historians are not relational or NoSQL databases; they have fewer capabilities and features and a much simpler structure.

However, they are designed and optimized for managing situations related to time series. They can acquire data...