Event Data Model in ATLAS

The event data model (EDM) of the ATLAS experiment is presented. For large collaborations like the ATLAS experiment common interfaces and data objects are a necessity to insure easy maintenance and coherence of the experiments software platform over a long period of time. The ATLAS EDM improves commonality across the detector subsystems and subgroups such as trigger, test beam reconstruction, combined event reconstruction and physics analysis. Furthermore the EDM allows the use of common software between online data processing and offline reconstruction. One important task of the EDM group is to provide know-how and the infrastructure to secure the accessibility of data even after changes to the data model. New processes have been put into place to manage the decoupling of the persistent (on disk) storage and the transient (in memory), and how to handle requests from developers to change or add to the stored data model.