... In order to realize the optimal scientific return from the VLT, ESO has undertaken to develop an end-to-end data flow system from proposal entry to science archive. The VLT Data Flow System (DFS) is being designed and implemented by the DFS Group (ESO Internal access only) in collaboration with VLT Division and Instrumentation Division . ... VLT Control System Interface . ... OBs are the quantum of data that flows within the DFS, collecting state, data and status information as they flow. ...