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From: kim@im4u.UUCP
Newsgroups: comp.databases
Subject: question
Message-ID: <1649@im4u.UUCP>
Date: Sun, 22-Mar-87 00:24:16 EST
Article-I.D.: im4u.1649
Posted: Sun Mar 22 00:24:16 1987
Date-Received: Sun, 22-Mar-87 16:31:07 EST
Organization: CSdept, UTaustin
Lines: 31
Keywords: hierarchical database query processing





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