On the Complexity of Database Queries 1 ... - Semantic Scholar
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On the Complexity of Database Queries 1 ... - Semantic Scholar
plexity classes spanned by these query languages range from AC0 to P, well within what is considered satisfactory in complexity theory. These tractability results ...
On the Complexity of Database Queries (Extended Abstract) Christos H. Papadimitriou
Division of Computer Science, U. C. Berkeley, Berkeley, CA 94720 Mihalis Yannakakis
Bell Laboratories, Lucent Technologies, Murray Hill NJ 07974
Abstract
We revisit the issue of the complexity of database queries, in the light of the recent parametric re nement of complexity theory. We show that, if the number of variables in the query (or the query size) is considered as a parameter, the familiar query languages (conjunctive, positive, rst order, Datalog) are classi ed 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. On the positive side, we show that this exponential dependence can be avoided for the extension of acyclic queries with = (but not
