http://doi.acm.org/10.1145/983070.983071 db/journals/sigmod/FolinusMS74.html Jeffrey J. Folinus Stuart E. Madnick Howard B. Schutzman Virtual Information in Data-Base Systems. 1-15 sigmodR/06-2/P001.pdf 1974 6 FDT - Bulletin of ACM SIGFIDET 2 db/journals/sigmod/sigmod6.html#FolinusMS74