25 th March 2003 V.Fine, H.Ma CHEP 2003, San Diego 1 Root Based Persistency in Athena (ATLAS) by Valeri Fine and Hong Ma

25 th March 2003 V.Fine, H.Ma CHEP 2003, San Diego 2 Persistency conversion services in Athena

25 th March 2003 V.Fine, H.Ma CHEP 2003, San Diego 3 Athena Converter Converters convert objects from one representation to another. (see: DRAFT/AthenaUserGuide.pdf ) DRAFT/AthenaUserGuide.pdf One particular use within Athena is to decouple algorithmic code from the underlying persistency mechanism or mechanisms. Thus a set of converters is provided to convert DataObjects within the transient stores to and from an equivalent set of persistent objects for each persistency implementation..

25 th March 2003 V.Fine, H.Ma CHEP 2003, San Diego 4 Conversion Process See: Athena. Chapter 15 Converters AthenaRootConverter AthenaRootAddress AthenaRootCnvSvc AthenaRootCnv

25 th March 2003 V.Fine, H.Ma CHEP 2003, San Diego 5 ROOT-base implementation

25 th March 2003 V.Fine, H.Ma CHEP 2003, San Diego 6 ROOT-based implementation (cont.) To facilitate the Athena-based production and the foreseen ROOT-based analysis and non-Athena based applications two extra software layers were deployed AthenaRootCnvSvcRootSvc IService RootKernel ROOT files

25 th March 2003 V.Fine, H.Ma CHEP 2003, San Diego 7 ROOT I/O for Athena algorithm and non-Athena applications AthenaRootCnvSvcRootSvc IService RootKernel ROOT files Athena Algorithm StoreGate GEANT 3ROOT macro libTable

25 th March 2003 V.Fine, H.Ma CHEP 2003, San Diego 8 Some implementation details Athena algorithms are well separated of any I/O technology and they are not affected by the concrete implementation details However non-Athena applications have no such shield and some knowledge about the file format are needed. The internal Object model of RootSvc class is inspired by STAR offline OO model ( see: The STAR offline framework Proceeding of ''CHEP'2000 Conference'', Padova, 2000 ) that defines hierarchical OO model of the generic named containers and provides a bunch of the classes to manipulate and navigate it.

25 th March 2003 V.Fine, H.Ma CHEP 2003, San Diego 9 Conclusion AthenaRoot Atlas package that provides the ROOT I/O Athena/Gaudi complaint layers have been developed and deployed. It is based on the ROOT Table library, organized in multiple levels. The top layer implements the Athena conversion interface, the bottom layer is only dependent on ROOT, and an intermediate level bridges these two layers. That allows the ROOT persistency for –any objects stored with the Athena StoreGate TDS providing the automatically generated Root converter classes –Any algorithm via RootSvc service –Any non-Athena application via RootKernel layer that is free of Athena framework dependency The package have been successfully tested with the various Atlas reconstruction / simulation applications and and was used during DC1 production