Re: database design method
Date: 9 Nov 2002 09:55:03 -0800
Message-ID: <e9d83568.0211090955.52e8b0ec_at_posting.google.com>
Jan,
> Another thing I wondered about while reading it is if I can express the
> NEST and the UNNEST operations of the nested relational algebra. I seem to
> remember that Date & Darwen were heavily opposed to those operations, but
> the language would otherwise be certainly computationally incomplete. So,
> can I?
I took a look at the printed version of TTM (2ed)
(which is not available on line).
On pages 137-138 there is a discussion of NEST and UNNEST
(in Tutorial-D the operations are called GROUP and UNGROUP).
So for the relationtype
RELATION { S# S#, PQ RELATION { P# P#, QTY QTY } }
RELATION { S# S#, P# P#, QTY QTY } with
(assuming SPQ1 is a relvar of the first type and SPQ2 is a relvar of the second type):
SPQ1 := SPQ2 GROUP { P#, QTY } AS PQ and the opposite operation would be
SPQ2 := SPQ1 UNGROUP PQ
regards,
Lauri Pietarinen
Received on Sat Nov 09 2002 - 18:55:03 CET