Athena is based on the common Gaudi framework that is used by ATLAS, LHCb and FCC.
Athena code is hosted in the CERN
GitLab service
where the repository owned by the atlas user plays a special
role as the repository from which all production releases
will be built. In the ATLAS development workflow this
repository is also the merge target for developments from
individual users or groups. There is much more information about
the development workflow in the ATLAS
git development tutorial.
While the athena repository contains any and all code that could be built
into an ATLAS software release, each release itself generally only
consists of a consistent subset of the code base. Each particular
build flavour is called a project and is steered from a particular
subdirectory of the Projects directory.
When a particular Athena project is built the build result encodes the
project name. Thus, independent of any release number, AthSimulation is
built from different code than AthAnalysisBase or AthDerivation. There is
an Athena project as well, which is a fairly complete build of almost
everything in the repository and is used to ensure that the
repository can be built consistently.
The main projects are:
| Project | Purpose |
| Athena | Functional for event generation, simulation, digitisation reconstruction and DAOD derivations (but rarely validated for anything except digi+reco) |
| AthenaP1 | Used to run the High Level Trigger and online monitoring at P1 |
| AthGeneration | For event generation |
| AthSimulation | For full Geant4 simulation |
| AthDerivation | For generating derived AODs from AOD and Athena based analysis |
| AthAnalysisBase | Athena based analysis |
| AnalysisBase | Non-athena ROOT based analysis |
Not all projects will exist, or be functional, in any particular
branch of the Athena repository. It should also be noted that although
the Athena project will be capable of running most workflows it
is not usually validated for anything outside of digitisation and
reconstruction (simulation may be validated, but in a different release
series). Thus exercise care and if you want to run event generation
or simulation then do ask the advice of the relevant group to ensure
you are working with a validated release and setup.