A historian is a type of database designed to archive automation and process data. Historians are used to troubleshoot processes, optimize manufacturing, store data for regulatory compliance, etc. Due to the enormous amount of data that they store, some historians reduce the total size of their database using various compression algorithms, such as storage by exception (only when data actually changes), or the Boxcar algorithm.

Historian products include AspenTech InfoPlus.21 (www.aspentech.com), Canary Labs Trend Historian (www.canarylabs.com), OSIsoft PI (www.osisoft.com), etc.