Chapter 12: Performance Evaluation of Logic Programs 461
than as relational algebra expressions, and the strategy is described in terms of
filters that are applied to the arcs of the graph. It is convenient to think of the
data as flowing through the graph along the arcs. A filter on an arc is a selec-
tion that can be applied to the tuples flowing through that arc, and is used to
reduce the number of tuples that are generated. Transforming a given rule/goal
graph into an equivalent graph with (additional) filters on some arcs is equiv-
alent to rewriting the corresponding set of rules.
The execution of a query starts with the nodes correspondin ...
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