The LHCb Detector Description Framework

A coherent O-O framework has been developed for describing the LHCb experimental apparatus to be used by the simulation, reconstruction and analysis applications. This framework is used for the realization of the detector data service, which is one of the main components of the GAUDI architecture in use in LHCb. Examples of detector description data are: the geometry and alignment parameters, the electronics calibration and their organization, the environmental parameters needed for the data processing, etc. The detector description data are made available to the physics algorithms through a number of transient objects. These transient objects are hierarchically organized and are a view of a global persistent representation, which is currently implemented using XML and takes into account versioning and a time validity interval. Other representations of the data are also provided to domain specific frameworks such as Geant4 and visualization components. We present the use-cases that have driven the development, the main design choices, and details of the first implementation of the framework. Finally we describe how it is customized to provide the specific needs of the various LHCb sub-detectors.