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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
154 Van
Gelder
DEFINITION 4
A general logic program is safe for negation if every top-down-positive
derivation has the property that any variable in a negative subgoal is also in
some positive subgoal of the same derived clause or in the top-level
clause.
The essential property of programs that are safe for negation is that when-
ever the top-level clause of a positive-complete derivation is variable free
(ground), then so is the last clause, which contains only negative subgoals (or
is empty). We see that this is not the case in P
2
above because there is a
positive-complete derivation that begins with p{\) and ends with
\s(l,Y).
However
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Publisher Resources

ISBN: 9781483221120