Optimization of a subclass of conjunctive queries
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.
KeywordsSymbol Mapping Query Evaluation Query Optimization Conjunctive Query Original Query
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- [ASU1]A.V.Aho, Y.Sagiv and J.D.Ullman, Efficient Optimization of a Class of Relational Expressions, ACM TODS, Vol 4, No 4, 1979.Google Scholar
- [ASU2]A.V.Aho, Y.Sagiv and J.D.Ullman, Equivalences among Relational Expressions, SIAM J. on Computing, Vol 8, No 2, 1979.Google Scholar
- [CM]A.Chandra and P.M.Merlin, Optimal Implementation of Conjunctive Queries in Relational Databases, Proc. of 9th ACM STOC, 1977.Google Scholar
- [Du]P.Dublish, Optimization and Expressibility of Relational Queries, Ph.D. Thesis, Dept. of Computer Science & Engg, IIT Delhi, 1988.Google Scholar
- [DM]P.Dublish and S.N.Maheshwari, An O(n2) Algorithm for Fan-Out Free Query Optimization, Proc. of the 7th Conf. on FST&TCS, Lec Notes in Computer Science, Vol 287, Springer Verlag, 1987.Google Scholar
- [GJ]M.Garey and D.S.Johnson, Computers and Intractability — A Guide to the Theory of NP-Completeness, W.H.Freeman, 1979.Google Scholar
- [JK]D.S.Johnson and A.Klug, Optimizing Conjunctive Queries that contain Untyped Variables, SIAM J. on Computing, Vol 12, No 4, 1983.Google Scholar
- [Ma]D.Maier, The Theory of Relational Databases, Computer Science Press, 1983.Google Scholar
- [Mu]B.N.S.Murthy, A Study of Complexity of some Optimization and Design Issues in Relational Database Systems, Ph.D. Thesis, Dept. of Electrical Engg, IIT Delhi, 1985.Google Scholar
- [Sa1]Y.Sagiv, Optimization of Queries in Relational Databases, UMI Research Press, 1981.Google Scholar
- [Sa2]Y.Sagiv, Quadratic Algorithms for Minimizing Joins in Restricted Relational Expressions, SIAM J. on Computing, Vol 12, No 2, 1983.Google Scholar
- [Ul]J.D.Ullman, Principles of Database Systems, Computer Science Press, 1982.Google Scholar