Ken-Chih Liu Rajshekhar Sunderraman A Generalized Relational Model for Indefinite and Maybe Information. 65-77 TKDE3/P0065.pdf 1991 3 IEEE Trans. Knowl. Data Eng. 1 db/journals/tkde/tkde3.html#LiuS91 db/journals/tkde/LiuS91.html conf/vldb/AbiteboulG85 conf/vldb/AbiteboulV84 ... journals/tods/BancilhonS81 conf/adbt/Biskup79 journals/tods/Biskup83 journals/fuin/Biskup84 journals/cacm/Codd70 ... journals/tods/Codd79 conf/pods/FaginUV83 journals/csur/GallaireMN84 journals/ipl/Grant77 journals/ipl/Grant79 journals/fuin/Grant80 conf/adbt/Imielinski82 conf/vldb/ImielinskiL81 conf/sigmod/ImielinskiL83 journals/jacm/ImielinskiL84 conf/pods/KuperUV84 conf/vldb/Lien79 journals/tods/Lipski79 journals/tods/LiuS90 conf/icde/LiuS88 ... conf/cade/Minker82 conf/db-workshops/Reiter82 journals/jacm/Reiter86 conf/sigmod/Vassiliou79 conf/vldb/Vassiliou80 journals/jcss/Zaniolo84