A. Campbell (DESY)
We present the scheme in use for online high level filtering, event reconstruction and classification in the H1 experiment at HERA since 2001. The Data Flow framework ( presented at CHEP2001 ) will be reviewed. This is based on CORBA for all data transfer, multi-threaded C++ code to handle the data flow and synchronisation and fortran code for reconstruction and event selection. A controller written in python provides setup,initialisation and process management. Specialised java programs provide run control and online access to and display of histograms. A C++ logger program provides central logging of standard printout from all processes. We show how the system handles online preparation and update of detector calibration and beam parameter data. Newer features are the selection of rare events for the online event display and the extension to multiple input sources and output channels. We dicuss how the system design provides automatic recovery from various failures and show the overall and long term performance. In addition we present the framework of event selection and classification and the features it provides.