Data Model ⇒ The CMS Event Data Model (EDM) is centered around the concept of an Event. Physically, an event is the result of a single readout of the detector electronics and the signals that will (in general) have been generated by particles, tracks, energy deposits, present in a number of bunch crossings. page

In software terms, an Event starts as a collection of the RAW data from a detector or MC event, stored as a single entity in memory, a C++ type-safe Container called edm::Event. An Event is a C++ object container for all RAW and reconstructed data related to a particular Collision [⇒ Hypertext Supercollaborator]. During processing, data are passed from one module to the next via the Event, and are accessed only through the Event. All objects in the Event may be individually or collectively stored in ROOT files, and are thus directly browsable in ROOT.

ROOT: analyzing petabytes of data, scientifically. site Installing ROOT