kim@im4u.UUCP (03/22/87)
Is it true that hierarchical database systems (such as IMS,System 2000) permit query qualification predicates to contain data items ONLY from record types that lie in a hierarchical path? Given a hierarchical schema: R1(A,B) / \ R2(C,D) R3(E,F) QUERY-1: GET R1.A WHERE (R2.C NOT.EQ. xx) AND (R3.E .EQ. yy) According to some literature, the query like QUERY-1 is not permitted because of its processing ambiguity(?). I don't see why. Can anyone clarify what the problem really is? Thank you in advance. Hyoung-Joo Kim University of Texas at Austin Department of Computer Sciences