Optimization of a subclass of conjunctive queries (extended abstract)

Authors:
Pratul Dublish;Joachim Biskup
Affiliations:
-;-
Venue:
ICDT '90 Proceedings of the third international conference on database theory on Database theory
Year:
1990

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Optimization of real conjunctive queries

PODS '93 Proceedings of the twelfth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems

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Abstract

The optimization problem for a subclass of conjunctive queries which is formed by the union of the class of fan-out free queries and a subclass of typed fan-out queries is investigated. The typed fan-out queries in this class are obtained from simple tableaux by allowing at most one attribute to violate the simple-tableau property. The optimization problem for several restricted subsets of typed fan-out queries is already known to be NP-hard. It is shown that the queries under consideration possess several useful properties which are then used to obtain an O(n2) optimization algorithm based on the implication graph technique. The optimization of typed fan-out queries, obtained from simple tableaux by allowing at most two attributes to violate the simple tableau property, is shown to be NP-hard.