conf/sigmod/76 Dennis G. Severance Guy M. Lohman Differential Files: Their Application to the Maintenance of Large Data Bases (Abstract). 43 1976 SIGMOD Conference db/conf/sigmod/sigmod76.html#SeveranceL76 http://doi.acm.org/10.1145/509383.509391 db/conf/sigmod/SeveranceL76.html SIGMOD76/P043.PDF