This document summarizes several models of media systems and communication flows, including Gieber and Johnson's source-reporter model and White's gatekeeping model.
Gieber and Johnson developed three models of relationships between reporters and their sources - separate roles, partially assimilated roles, and fully assimilated roles. White's gatekeeping model shows how news items pass through different "gates" or decision points, with some items being selected for further dissemination and others being rejected by gatekeepers such as editors. McNelly later expanded on White's model by proposing that there are multiple gatekeepers at different stages rather than just one.