Acta Informatica

, Volume 55, Issue 1, pp 17–56 | Cite as

Conjunctive query containment over trees using schema information

  • Henrik Björklund
  • Wim Martens
  • Thomas Schwentick
Original Article


We study the containment, satisfiability, and validity problems for conjunctive queries over trees with respect to a schema. We show that conjunctive query containment and validity are 2EXPTIME -complete with respect to a schema, in both cases where the schema is given as a DTD or as a tree automaton. Furthermore, we show that satisfiability for conjunctive queries with respect to a schema can be decided in NP . The problem is NP -hard already for queries using only one kind of axis. Finally, we consider conjunctive queries that can test for equalities and inequalities of data values. Here, satisfiability and validity are decidable, but containment is undecidable, even without schema information. On the other hand, containment with respect to a schema becomes decidable again if the “larger” query is not allowed to use both equalities and inequalities.



This work was supported by grant number MA 4938/2-1 from the Deutsche Forschungsgemeinschaft (Emmy Noether Nachwuchsgruppe) and the Swedish Research Council Grant 621-2011-6080.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  • Henrik Björklund
    • 1
  • Wim Martens
    • 2
  • Thomas Schwentick
    • 3
  1. 1.Department of Computing ScienceUmeå UniversityUmeåSweden
  2. 2.Institut für InformatikUniversität BayreuthBayreuthGermany
  3. 3.Department of Computer ScienceTechnische Universität DortmundDortmundGermany

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