Theory of Computing Systems

, Volume 52, Issue 3, pp 483–541 | Cite as

Relaxed Notions of Schema Mapping Equivalence Revisited

  • Reinhard Pichler
  • Emanuel Sallinger
  • Vadim Savenkov


Recently, two relaxed notions of equivalence of schema mappings have been introduced, which provide more potential of optimizing schema mappings than logical equivalence: data exchange (DE) equivalence and conjunctive query (CQ) equivalence. In this work, we systematically investigate these notions of equivalence for mappings consisting of s-t tgds and target egds and/or target tgds. We prove that both CQ- and DE-equivalence are undecidable and so are some important optimization tasks (like detecting if some dependency is redundant). However, we also identify an important difference between the two notions of equivalence: CQ-equivalence remains undecidable even if the schema mappings consist of s-t tgds and target dependencies in the form of key dependencies only. In contrast, DE-equivalence is decidable for schema mappings with s-t tgds and target dependencies in the form of functional and inclusion dependencies with terminating chase property.


Data integration Schema mapping optimization Equivalence of schema mappings 


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Copyright information

© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  • Reinhard Pichler
    • 1
  • Emanuel Sallinger
    • 1
  • Vadim Savenkov
    • 1
  1. 1.Vienna University of TechnologyViennaAustria

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