Who invitented the division operator in relational algebra and why?

From: (wrong string) åg <amund_at_texassibir.com>
Date: Tue, 15 Apr 2003 13:07:31 +0200
Message-ID: <b7gotv$2d85$1_at_toralf.uib.no>



Hi DB-theorists!

The division operator in relational algebra is not part of the minimal set of operators (select, project, union, minus and cartesian product). Join was added to relational algebra because it was a practical operator was used a lot in practise. Although join can be performed with a combination of the minimal set, it was a simpler way of doing the common operation that joining relations is.

Does anyone have references to the first article where the division operator was "made"? The division operator can make universal queries, but can it do all queries? Is it possible to formulate the query: 'Find employees that work on all the projects of its own department' with the division operator?

I will be very greatful if someone has any pointers to some or all of these questions, as I am doing a literature study prior to a thesis project, and I am having some trouble finding out the why's of the division operator.

Cheers, and Happy Easter from
Amund Trovåg Received on Tue Apr 15 2003 - 13:07:31 CEST

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