[comp.databases] question

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