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Optimization using tuple subsumption

  • Venky Harinarayan
  • Ashish Gupta
Contributed Papers Constraints and Dependencies
Part of the Lecture Notes in Computer Science book series (LNCS, volume 893)

Abstract

A tuple t1 of relation R subsumes tuple t2 of R, with respect to a query Q if for every database, tuple t1 derives all, and possibly more, answers to query Q than derived by tuple t2. Therefore, the subsumed tuple t2 can be ignored with respect to Q in the presence of tuple t1 in relation R. This property finds use in a large number of problems. For instance: during query optimization subsumed tuples can be ignored thereby avoiding the computation of redundant answers; the size of cached information in distributed and object oriented systems can be reduced by omitting subsumed tuples; constraints need not be checked and rules need not be recomputed when provably subsumed updates are made. We give algorithms for deciding efficiently when a tuple subsumes another tuple for queries that use arbitrary mathematical functions. We characterize queries for which, whenever a set of tuples T subsumes a tuple t then one of the tuples in T also subsumed t, yielding efficiently verifiable cases of subsumption.

Keywords

Distinguished Point Integrity Constraint Query Optimization Constraint Language Constraint Check 
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 1995

Authors and Affiliations

  • Venky Harinarayan
    • 1
  • Ashish Gupta
    • 2
    • 3
  1. 1.Department of Computer ScienceStanford UniversityCA
  2. 2.Department of Computer ScienceStanford
  3. 3.IBM Almaden Research CenterUSA

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