MESSAGE
| DATE | 2014-12-11 |
| FROM | Ruben Safir
|
| SUBJECT | Subject: [LIU Comp Sci] Database Class concepts which are still unclear
|
From owner-learn-outgoing-at-mrbrklyn.com Thu Dec 11 11:03:45 2014
Return-Path:
X-Original-To: archive-at-mrbrklyn.com
Delivered-To: archive-at-mrbrklyn.com
Received: by mrbrklyn.com (Postfix)
id E596E161160; Thu, 11 Dec 2014 11:03:44 -0500 (EST)
Delivered-To: learn-outgoing-at-mrbrklyn.com
Received: by mrbrklyn.com (Postfix, from userid 28)
id C9629161166; Thu, 11 Dec 2014 11:03:44 -0500 (EST)
Delivered-To: learn-at-nylxs.com
Received: from mailbackend.panix.com (mailbackend.panix.com [166.84.1.89])
by mrbrklyn.com (Postfix) with ESMTP id D0A37161160
for ; Thu, 11 Dec 2014 11:03:42 -0500 (EST)
Received: from [10.0.0.42] (unknown [96.57.23.82])
by mailbackend.panix.com (Postfix) with ESMTPSA id 6BDF513C33;
Thu, 11 Dec 2014 11:03:41 -0500 (EST)
Message-ID: <5489C062.7010909-at-panix.com>
Date: Thu, 11 Dec 2014 11:03:46 -0500
From: Ruben Safir
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0
MIME-Version: 1.0
To: learn-at-nylxs.com, Ping-Tsai Chung
Subject: [LIU Comp Sci] Database Class concepts which are still unclear
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit
Sender: owner-learn-at-mrbrklyn.com
Precedence: bulk
Reply-To: learn-at-mrbrklyn.com
6.2.2 The CARTESIAN PRODUCT (CROSS PRODUCT)
Operation
Next, we discuss the CARTESIAN PRODUCT operation—also known as CROSS
PRODUCT or CROSS JOIN—which is denoted by ×. This is also a binary set
opera-
tion, but the relations on which it is applied do not have to be union
compatible. In
its binary form, this set operation produces a new element by combining
every
member (tuple) from one relation (set) with every member (tuple) from
the other
relation (set). In general, the result of R(A1, A2, ..., An) × S(B1, B2,
..., Bm) is a rela-
tion Q with degree n + m attributes Q(A1, A2, ..., An, B1, B2, ..., Bm),
in that order.
The resulting relation Q has one tuple for each combination of
tuples—one from R
and one from S. Hence, if R has nR tuples (denoted as |R| = nR), and S
has nS tuples,
then R × S will have nR * nS tuples.
The n-ary CARTESIAN PRODUCT operation is an extension of the above concept,
which produces new tuples by concatenating all possible combinations of
tuples
from n underlying relations.
What is an n-ary operation? It is mentioned several times, but I don't
see an answer
Ruben
|
|
