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Foundations of Deductive Databases and Logic Programming
book

Foundations of Deductive Databases and Logic Programming

by Jack Minker
May 2014
Intermediate to advanced content levelIntermediate to advanced
752 pages
35h 3m
English
Morgan Kaufmann
Content preview from Foundations of Deductive Databases and Logic Programming
Chapter 8: Intelligent Query Answering
285
JOIN
Let
Tj
and r
2
be two rules defined for relations R and S.
In order to determine the transformability of these rules we have to deter-
mine when the following holds:
r
1
(R)Mr
2
(S)
= r
Q
(RMS)
Let X = Υ Π Ζ be the common set of attributes for R and S. In order for
the above equality to hold, the following necessary and sufficient conditions
must be satisfied:
7r
x
(rj(R))
=
TT
X
(R)
and
ir
x
(r
2
(S))
=
TT
X
(S)
for every R and S (1)
Condition 1 means that rules τ
χ
and r
2
leave the projection on X of R and S
invariant. Indeed, otherwise rules r
t
and r
2
could produce some tuples which
would contribute to the joi ...
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Publisher Resources

ISBN: 9781483221120