John Grant, Jack Minker Optimization in Deductive and Conventional Relational Database Systems. [Citation Graph (25, 0)][DBLP] Advances in Data Base Theory, 1979, pp:195-234 [Conf]
John Grant, Jack Minker Answering Queries in Indefinite Databases and the Null Value Problem. [Citation Graph (9, 0)][DBLP] Advances in Computing Research, 1986, v:3, n:, pp:247-267 [Journal]