The group has three sections: CMG-DS, CMG-OS and CMG-CO.

DS stands for "Detector Software", though a name that does more justice to it is "Detector Systems". Its activity is mainly organised around software (reconstruction, simulation, performance, and physics studies) for CMS Phase 2 (HL-LHC) detector upgrades and a number of people participate in the HGCAL (High-Granularity Calorimeter) including areas close to the detector systems (Silicon sensors, Modules, Electronics).

OS stands for "Online Selection" and is primarily concerned with the upgrade of the Level-1 trigger of CMS -- also for the HL-LHC era. Here, CMG is one of the leading groups working on "Particle Flow at Lvl-1 trigger". 

CO stands for "Computing", and the section is responsible for several central computing services for the CMS experiment in the area of data management and database interfaces. 

The organigram of the EP-CMG group (dynamically generated version) can be found at this HR web page.