Hasse and Post determined that the most readily determined descriptor for Government publications was their origin or authorship, generally expressed not as a personal author but as agency, bureau, or office. In the scheme, each department in the Executive, Judicial, and Legislative Branches, and each independent agency, is assigned an alphabetic symbol, generally although not strictly, mnemonic; thus, A is Agriculture Department, C is Commerce, S is State Department. In later practice two- and three letter symbols have been used as necessary, so FS for Federal Security Agency (in the 1930s), HE for Health, Education, and Welfare, later transferred to Health and Human Services, NAS for NASA, and HS for Homeland Security. Congress and its committees and commissions are designated X and Y.
Basing the classification on the current federal government organization causes a problem when agencies and bureaus are created or relocated. For example, the Department of Homeland Security was established in 2002, and took bureaus/subordinate offices from Treasury, Defense, Justice, and several others, as well as incorporated the formerly independent agency FEMA (Federal Emergency Management Administration).