conf/sigmod/77 Paolo Paolini Giuseppe Pelagatti Formal Definition of Mappings in a Data Base. 40-46 1977 SIGMOD Conference db/conf/sigmod/sigmod77.html#PaoliniP77 http://doi.acm.org/10.1145/509404.509413 SIGMOD77/P040.PDF ... journals/cacm/Codd70 ... journals/acta/Hoare72 ... ...