Detector Description Framework in LHCb

The Gaudi architecture and framework are designed to provide a common infrastructure and environment for simulation, filtering, reconstruction and analysis applications. In this context, a Detector Description Service was developed in LHCb in order to also provide easy and coherent access to the description of the experimental apparatus. This service centralizes every information about the detector, including geometry, materials, alignment, calibration, structure and controls. From the proof of concept given by the first functional implementation of this service late 2000, the Detector Description Service has grown and has become one of the major components of the LHCb software, shared among all applications, including simulation, reconstruction, analysis and visualization. We describe here the full and functional implementation of the service. We stress the easiness of customization and extension of the detector description by the user, on the seamless integration with condition databases in order to handle time dependent data and on the choice of XML as a persistency back-end for LHCb Detector data. We show how the detector description can be shared but still contains application specific data and keeps at the same time several levels of granularity. We present several external tools which provide additional value to the Detector Description Service like a dedicated, easy to use XML editor and different geometry checkers. We finally give hints on how this service could evolve to be part of a common effort between all LHC experiments that would aim at defining common Detector description tools at the level of the LCG project.