The VLT Data Flow System, a flexible science support operations engine

The Data Flow System (DFS) supports the science operation model which is in place for the ESO Very Large Telescope in order to globally maximise its efficiency and ensure a high and predictable data quality level. It is a system which handles all necessary components involved in the observation life-cycle. Although after some four years of operation, the basic framework of DFS can be considered as ’complete’, the implementation of new improvements and enhancements is a neverending process due to the appearance of new observing facilities, changing hardware and software standards, and also due to feedback coming from our various users, namely the operations teams at Paranal, La Silla, at the ESO headquarters as well as external astronomers from their home institutes. This article describes how new requirements are addressed to maintain a good level of performance, together with keeping maintenance costs low. In particular, it explains how the organisation and the Software Engineering process put in place for that project makes it possible to have a robust, efficient and flexible ‘science support engine’, without which it would be difficult, if not impossible, to operate the ESO telescopes.