Optimization of a subclass of conjunctive queries

  • Pratul Dublish
  • Joachim Biskup
  • Yehoshua Sagiv
Part of the Lecture Notes in Computer Science book series (LNCS, volume 470)


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.


Symbol Mapping Query Evaluation Query Optimization Conjunctive Query Original Query 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag Berlin Heidelberg 1990

Authors and Affiliations

  • Pratul Dublish
    • 1
  • Joachim Biskup
    • 1
  • Yehoshua Sagiv
    • 2
  1. 1.Institut für InformatikUniversität HildesheimHildesheimWest Germany
  2. 2.Hebrew University and Stanford UniversityGermany

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