conf/vldb/81 Tomasz Imielinski Witold Lipski Jr. On Representing Incomplete Information in a Relational Data Base VLDB81/P388.PDF 388-397 1981 VLDB db/conf/vldb/vldb81.html#ImielinskiL81 journals/siamcomp/AhoSU79 conf/adbt/Biskup79 journals/cacm/Codd70 ... journals/tods/Codd79 books/fm/GareyJ79 journals/ipl/Grant77 books/cs/HorowitzS78 ... conf/pods/ImielinskiL82 ... journals/tods/Lipski79 journals/jacm/Lipski81 conf/adbt/Reiter77 ... books/cs/Ullman80 conf/sigmod/Vassiliou79 conf/vldb/Vassiliou80 conf/focs/YannakakisP80 ...