Optimizing Conjunctive Queries over Trees Using Schema Information

  • Henrik Björklund
  • Wim Martens
  • Thomas Schwentick
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 5162)


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 w.r.t. a schema (DTD or Relax NG). Furthermore, we show that satisfiability for conjunctive queries w.r.t. 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 w.r.t. a schema becomes decidable again if the “larger” query is not allowed to use both equalities and inequalities.


Conjunctive Query Tree Automaton Schema Information XPath Query XPath Expression 
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Copyright information

© Springer-Verlag Berlin Heidelberg 2008

Authors and Affiliations

  • Henrik Björklund
    • 1
  • Wim Martens
    • 1
  • Thomas Schwentick
    • 1
  1. 1.Technical University of Dortmund 

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