Solving Queries by Tree Projections

Yehoshua Sagiv, Oded Shmueli

Research output: Contribution to journalArticlepeer-review

18 Scopus citations

Abstract

Suppose a database schema D is extended to D¯ by adding new relation schemas, and states for D are extended to states for D¯ by applying joins and projections to existing relations. It is shown that certain desirable properties that D¯ has with respect to D. These properties amount to the ability to compute efficiently the join of all relations in a state for D from an extension of this state over D¯. The equivalence is proved for unrestricted 1993 databases. If D¯ is obtained from D by adding a set of new relation schemas that form a tree schema, then the equivalence also holds for finite databases. In this case there is also a polynomial time algorithm for testing the existence of a tree projection of D¯ with respect to D.

Original languageEnglish
Pages (from-to)487-511
Number of pages25
JournalACM Transactions on Database Systems
Volume18
Issue number3
DOIs
StatePublished - 9 Jan 1993

Keywords

  • Acyclicity
  • chase
  • database schema
  • hypergraph
  • inclusion dependency
  • join
  • monotone join expression
  • projection
  • qual graph
  • relational database
  • semijoin
  • semijoin reduction
  • tableau
  • tree projection
  • tree schema

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