Primary Numbers Database for ATLAS Detector Description Parameters

We present the design and the status of the database for detector description parameters in ATLAS experiment. The relational database for storing these “Primary Numbers” is based on the technology developed by some of the authors in the earlier project NOVA [1]. The ATLAS Primary Numbers are the parameters defining the detector geometry and digitization in simulations, as well as certain reconstruction parameters, including the identifier maps of the detector elements. Since the detailed ATLAS detector description needs more than 10,000 such parameters, a preferred solution is to have a single verified source for all these data. As a first approximation these parameters fit well into the structured name-value pair concept. A more detailed view of the parameter provides not only the parameter name and the value but also the parameter type (int, float,...), the textual comment describing the parameter meaning, the parameter scope (representing the structural container that this parameter belongs to), and may include additional information on the parameter unit of measurement and the parameter version. Effectively, the database stores the data dictionary for each parameter collection object, providing schema evolution support for object-based retrieval of parameters. The same Primary Numbers are served to many different clients accessing the database: the ATLAS software framework Athena, the Geant3 heritage framework Atlsim, the Geant4 developers’ framework FADS/Goofy, the generator of XML output for detector description, and several end-user clients for interactive data navigation, including web-based browsers and ROOT. The preferred mode of access to these data is via connections to Athena services (conversion and conditions/transient stores). Another access mode is implemented through the interval-of-validity service for timestamp-based data retrieval within the conditions database. The choice of the MySQL database product for the implementation provides additional benefits: the Primary Numbers database can be used on the developers’ laptop when disconnected (using the MySQL embedded server technology), with data being updated when the laptop is connected (using the MySQL database replication).