Levels of Subject Authority Control 

Subject authority control is exercised at two levels: central and local. At the central level, a central agency (e.g. Library of Congress) maintains the subject authority file (in card or machine-readable form) or subject heading list (in print form) and makes changes to existing headings and cross-references as well as adding new ones. 

On local level, a library devises such  a means, which ensures conformity and currency of the subject libraries following one of the standard lists of subject headings (e.g. LCSH or Sear's List). It creates local subject authority records only for headings not yet appearing in established  headings in a subject heading list along with needed maintenance information. Thus, the subject authority control at the local level includes correcting erroneous headings and cross-references, updating obsolete headings, and adding or revising cross-references necessitated by new headings.