The development of the ROOT data analysis system

The previous generation of data analysis systems such as PAW had been designed as stand-alone executable modules to be used in the final stage of data analysis. This conventional model has been used very successfully to display histograms or generate histograms on the fly from some ntuple files. It had the advantage to be totally independent of any framework used in the simulation, reconstruction or physics analysis steps. With the advent of Object-Oriented programming, this simple model appears to be insufficient. The ROOT system has been designed to provide all the facilities in a system like PAW, but in addition has the ambition to provide a complete and coherent framework that can be used at all stages of data processing and well matched to the OO paradigm.