industrial//industrial data layer//historian

A **process historian** is a database specialized in industrial time-based data: millions or billions of samples of tag, timestamp, value and quality. Historic names: OSIsoft PI, now AVEVA PI; AspenTech IP.21.

A process historian is a database specialized in industrial time-based data: millions or billions of samples of tag, timestamp, value and quality. Historic names: OSIsoft PI, now AVEVA PI; AspenTech IP.21.

Its classic trait is compression: it does not necessarily store every sample when the value barely changes. A temperature reading 100.000, 100.001, 100.002, 100.000, 100.001 is five nearly identical points; a deadband or swinging-door algorithm keeps the shape of the signal with a fraction of the storage.

It is the archive behind every trend on a SCADA screen and the raw material of any later analysis. It coexists with, rather than being replaced by, the modern time-series database: historian, data lake or cloud, TSDB and SQL each keep a role in a real plant.

What it stores is the tag; what it usually lacks is the business context that makes a tag comparable across lines or plants (data contextualization).