Historians, by definition, act as data concentrators. They collect data from different field devices, micro-controllers, and PLCs that control different working lines or functional areas of the plant, and SCADA systems. Historian databases are typically structured and linked to a structured asset model. This makes it easier to identity and recognize the data flow that the I-IoT data stream is interested in. Like SCADA, they need to communicate with the MES and ERP systems so they are usually connected to the plant or the corporate network, which again simplifies the effort of transferring the data to the cloud over the internet. In general, they are quite reliable compared to SCADA systems because their connectors, which gather data from different data sources, have built-in data buffering abilities and store-and-forward mechanisms. This means that, in general, they are quite resilient to network instability or unexpected downtime of the Historian server. The reliability of the data that is stored in the Historian depends almost entirely on the availability and reliability of the device from which the data comes.