A data Historian is a software solution that allows the user to replay entire process sequences, for instance to analyze a particular behavior. The datasets put into play are at once functionally coherent and technically different, which means they must be very precisely captured and recorded. Any types of data can be involved, including digital and analog values, information about alarms, aggregations and statistical calculations, as well as information about equipment and the quality of the running of the processes themselves. Furthermore, these recordings have to be picked up from a very different types of data sources, such as PLCs, DCSs, RTUs, proprietary interfaces on machines or measuring instruments and third-party computer systems as well as manually entered data. The dataset is stored chronologically on appearance or execution such as to reduce retrieval times to a minimum and to maximize data reliability. The concepts of timestamping and performance are therefore central to running a data historian.