Integration of Geant4 with the Gaudi Framework

The GAUDI software framework is to be used for all event-processing applications in the LHCb experiment.The GEANT4 toolkit has been integrated into GAUDI to form the basis of the LHCb simulation program GAUSS.The benefits of this approach are that it permits re-use of basic services,such as persistency,interactivity and data visualization,as well as physics algorithms that were originally developed in the context of the reconstruction and analysis programs.Following the GAUDI philosophy,the integration has been achieved by developing a number of services with abstract interfaces that can be plugged in at run-time.We describe the overall design and details of the components for interfacing the detector geometry,the primary interaction and the output from tracking particles through the detector.