Ken-Chih Liu Rajshekhar Sunderraman Indefinite and Maybe Information in Relational Databases. 1-39 TODS15/P001.PDF 1990 15 ACM Trans. Database Syst. 1 db/journals/tods/tods15.html#LiuS90 http://doi.acm.org/10.1145/77643.77644 db/journals/tods/LiuS90.html journals/tods/Biskup83 ... journals/cacm/Codd70 journals/csur/GallaireMN84 journals/ipl/Grant79 ... journals/acr/GrantM86 conf/adbt/Imielinski82 conf/vldb/ImielinskiL81 journals/tods/Lipski79 conf/ismis/LiuS87 conf/cade/Minker82 conf/cade/MinkerP84 ... journals/jacm/Reiter86 books/cs/Ullman82 journals/jcss/Zaniolo84