Bibliographic Classification using the ADS Databases
  We discuss two techniques used to characterize bibliographic records based on their similarity to and relationship with the contents of the NASA Astrophysics Data System (ADS) databases. The first method has been used to classify input text as being relevant to one or more subject areas based on an analysis of the frequency distribution of its individual words. The second method has been used to classify existing records as being relevant to one or more databases based on the distribution of the papers citing them. Both techniques have proven to be valuable tools in assigning new and existing bibliographic records to different disciplines within the ADS databases. 
Alberto Accomazzi, Michael J. Kurtz, Guenther Eichhorn, Edwin   Henneken, Carolyn S. Grant, Markus Demleitner, Stephen S. Murray