In the core public administration classification system, we refer to the organization of work and employees as the occupational group structure. Occupational groups are designated by a two-letter abbreviation that is shorthand for the occupational group’s title (e.g. “FS” stands for the Foreign Service group). The number assigned to the occupational group designator refers to the level within the group (e.g. the first level of the FS group is FS-1).