  A Geant4-based simulation framework for rare event searching experiments with
germanium detectors named SAGE is presented with details. It is designed for
simulating, assessing, analyzing background components and investigating the
response of the germanium detectors. The SAGE framework incorporates its
experiment-specific geometries and custom attributes, including the event
generator, physical lists and output format, to satisfy various simulation
objectives. Its docker image has been prepared for virtualizing and
distributing the SAGE framework. Deployment a Geant4-based simulation will be
convenient under this docker image. The implemented geometries include both the
p-type point contact and broad energy germanium detectors with environmental
surroundings, and these hierarchical geometries can be easily extended. Users
select these custom attributes via the JSON configuration file. The
aforementioned attributes satisfy the simulation demands and make SAGE become a
generic and powerful simulation framework for CDEX experiment.
