conf/sigmod/78 R. M. Lee Rob Gerritsen Extended Semantics for Generalization Hierarchies. 18-25 1978 SIGMOD Conference db/conf/sigmod/sigmod78.html#LeeG78 SIGMOD78/P018.PDF http://doi.acm.org/10.1145/509252.509263 db/conf/sigmod/LeeG78.html journals/cacm/Codd70 persons/Codd71a persons/Codd72 conf/vldb/EswaranC75 conf/vldb/HammerM75 ... ... journals/tods/SmithS77 ... ... ... ... ...