An application framework and data model prototype for the BaBar experiment

The BaBar experiment is a high energy physics experiment to do physics with e+e- colliding beams in the 10 GeV center-of-mass energy at the PEP-II accelerator at the Stanford Linear Accelerator Center. The principal objectives are to study CP violation and rare processes in decays of B mesons. The experiment is under construction, with first data anticipated in 1999. The BaBar experiment is expected to accumulate of order 109 events per calendar year, with over 108 interesting hadronic events. The data must be stored efficiently, but must be easily accessible in order for multiple and frequent physics analyses to be carried out. The analysis framework must be flexible enough to accommodate a variety of analysis modules and multiple input/output streams. The BaBar collaboration has developed a prototype for the analysis framework and data access, written in C++ using an object-oriented design philosophy. The data access is based on the Farfalla package. The base class is a ''node''. Various types of node objects can be associated into a ''tree'' organization to form the record of an event. Because of an existing Fortran code base and expertise, access from Fortran 90 as well as C++ is a requirement, and various implementations have been studied. The analysis framework is intended to be a system which can accommodate code from a variety of sources in both online and offline environments. The prototype is based on the idea of forming sequences of modules which can be linked together to obtain the desired processing of data streams. There are standard modules, which perform tasks such as input, output and filtering. In addition, the user can create modules for particular analysis needs. A complete execution sequence, called a path, can be active or inactive, or can be terminated prior to completion based on the event data in the filtering process. Multiple paths can be specified