On the Complexity of Database Queries.

Christos H. Papadimitriou, Mihalis Yannakakis: On the Complexity of Database Queries. PODS 1997: 12-19
  author    = {Christos H. Papadimitriou and
               Mihalis Yannakakis},
  title     = {On the Complexity of Database Queries},
  booktitle = {Proceedings of the Sixteenth ACM SIGACT-SIGMOD-SIGART Symposium
               on Principles of Database Systems, May 12-14, 1997, Tucson, Arizona},
  publisher = {ACM Press},
  year      = {1997},
  isbn      = {0-89791-910-6},
  pages     = {12-19},
  ee        = {, db/conf/pods/PapadimitriouY97.html},
  crossref  = {DBLP:conf/pods/97},
  bibsource = {DBLP,}


We revisit the issue of the complexity of database queries, in the light of the recent parametric refinement of complexity theory. We show that, if the query size (or the number of variables in the query) is considered as a parameter, then the relational calculus and its fragments (conjunctive queries, positive queries) are classified at appropriate levels of the so-called W hierarchy of Downey and Fellows. These results strongly suggest that the query size is inherently in the exponent of the data complexity of any query evaluation algorithm, with the implication becoming stronger as the expressibility of the query language increases. For recursive languages (fixpoint logic, Datalog) this is provably the case [14]. On the positive side, we show that this exponential dependence can be avoided for the extension of acyclic queries with != (but not <) inequalities.

Copyright © 1997 by the ACM, Inc., used by permission. Permission to make digital or hard copies is granted provided that copies are not made or distributed for profit or direct commercial advantage, and that copies show this notice on the first page or initial screen of a display along with the full citation.

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Proceedings of the Sixteenth ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems, May 12-14, 1997, Tucson, Arizona. ACM Press 1997, ISBN 0-89791-910-6
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Rodney G. Downey, Michael R. Fellows: Fixed-Parameter Tractability and Completeness I: Basic Results. SIAM J. Comput. 24(4): 873-921(1995) BibTeX
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Referenced by

  1. Georg Gottlob, Nicola Leone, Francesco Scarcello: Hypertree Decompositions and Tractable Queries. PODS 1999: 21-32
  2. Sergei G. Vorobyov, Andrei Voronkov: Complexity of Nonrecursive Logic Programs with Complex Values. PODS 1998: 244-253
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