The VLDB Journal

, Volume 25, Issue 3, pp 381–397

Mapping-equivalence and oid-equivalence of single-function object-creating conjunctive queries

  • Angela Bonifati
  • Werner Nutt
  • Riccardo Torlone
  • Jan Van den Bussche
Regular Paper

DOI: 10.1007/s00778-016-0421-x

Cite this article as:
Bonifati, A., Nutt, W., Torlone, R. et al. The VLDB Journal (2016) 25: 381. doi:10.1007/s00778-016-0421-x


Conjunctive database queries have been extended with a mechanism for object creation to capture important applications such as data exchange, data integration, and ontology-based data access. Object creation generates new object identifiers in the result that do not belong to the set of constants in the source database. The new object identifiers can be also seen as Skolem terms. Hence, object-creating conjunctive queries can also be regarded as restricted second-order tuple-generating dependencies (SO-tgds), considered in the data exchange literature. In this paper, we focus on the class of single-function object-creating conjunctive queries, or sifo CQs for short. The single-function symbol can be used only once in the head of the query. We give a new characterization for oid-equivalence of sifo CQs that is simpler than the one given by Hull and Yoshikawa and places the problem in the complexity class NP. Our characterization is based on Cohen’s equivalence notions for conjunctive queries with multiplicities. We also solve the logical entailment problem for sifo CQs, showing that also this problem belongs to NP. Results by Pichler et al. have shown that logical equivalence for more general classes of SO-tgds is either undecidable or decidable with as yet unknown complexity upper bounds.


Conjunctive query Object creation Oid Equivalence Logical entailment SO-tgd Sifo CQ Nested tgd Schema mapping 

Copyright information

© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  • Angela Bonifati
    • 1
  • Werner Nutt
    • 2
  • Riccardo Torlone
    • 3
  • Jan Van den Bussche
    • 4
  1. 1.LIRISUniversity of Lyon 1LyonFrance
  2. 2.Free University of Bozen-BolzanoBolzanoItaly
  3. 3.Università Roma TreRomeItaly
  4. 4.Hasselt University and Transnational University of LimburgHasseltBelgium

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