Database architecture for the calibration of ATLAS monitored drift tube chambers

Experiments at the CERN Large Hadron Collider (LHC) 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 calibration of the 375000 monitored drift tubes used for precision tracking in the muon spectrometer of the ATLAS experiment. Data suitable for MDT calibration will be extracted from the second level trigger and then streamed to three remote tier-2 calibration centres. At each centre, the computation of the actual calibration 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 central database located at CERN using ORACLE streams. 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. Calibration sites will also need to access the ATLAS conditions data that are relevant for the calculation of MDT calibrations: part of the conditions database will thus be replicated at the remote sites via ORACLE streams. This paper reviews the complex chain of databases envisaged to support the MDT calibration and describes the actual status of the implementation and of the tests that are being performed to ensure a smooth operation at the LHC start-up in 2008.