Database architecture for the calibration of ATLAS Monitored Drift Tube Chambers

The size and complexity of LHC experiments raise unprecedented challenges not only in terms of detector design, construction and operation, but also in terms of software models and data persistency. One of the more challenging tasks is the calibra tion of the 375000 Monitored Drift Tubes, that will be used as precision tracking detectors in the Muon Spectrometer of the ATLAS experiment. A high rate of muon tracks is needed to reach the design average resolution of 80 microns. In this context, data suitable for MDT calibration will be extracted from the second level trigger and then streamed to three remote Tier-2 Calibration Centers. The Calibration sites will also need the ATLAS conditions data that are relevant for the calculation of MDT calibrat ions: either the appropriate tables of the Conditions Database will be replicated at the remote sites via ORACLE streams, or the remote sites will directly access these tables from the nearest Tier-1. At each centre, the computation of the actual calibrat ion constants will be performed in several steps, including strict validation and data quality checks. All information produced at every stage of the calibration procedure will be stored in local ORACLE Calibration databases that will be replicated to a c entral database located at CERN using ORACLE streams: this will allow each Calibration site to access the data produced by the others and to eventually provide back-up should one site become unavailable for any reason. The validated calibration constants will be extracted from the CERN Calibration DB and stored into the ATLAS Conditions database for subsequent use in reconstruction and data analysis. This paper reviews the complex chain of databases envisaged to support the MDT Calibration and describes t he actual status of the implementation and the tests that are being performed to ensure a smooth operation at the LHC start-up at the end of this year