A Study of a Positive Fragment of Path Queries: Expressiveness, Normal Form, and Minimization

  • Yuqing Wu
  • Dirk Van Gucht
  • Marc Gyssens
  • Jan Paredaens
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 5588)

Abstract

We study the expressiveness of a positive fragment of path queries, denoted Path\(\mathstrut^+\), on node-labeled trees documents. The expressiveness of Path\(\mathstrut^+\) is studied from two angles. First, we establish that Path\(\mathstrut^+\) is equivalent in expressive power to a particular sub-fragment as well as to the class of tree queries, a sub-class of the first-order conjunctive queries defined over label, parent-child, and child-parent predicates. The translation algorithm from tree queries to Path\(\mathstrut^+\) yields a normal form for Path\(\mathstrut^+\) queries. Using this normal form, we can decompose a Path\(\mathstrut^+\) query into sub-queries that can be expressed in a very small sub-fragment of Path\(\mathstrut^+\) for which efficient evaluation strategies are available. Second, we characterize the expressiveness of Path\(\mathstrut^+\) in terms of its ability to resolve nodes in a document. This result is used to show that each tree query can be translated to a unique, equivalent, and minimal tree query. The combination of these results yields an effective strategy to evaluate a large class of path queries on documents.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2009

Authors and Affiliations

  • Yuqing Wu
    • 1
  • Dirk Van Gucht
    • 1
  • Marc Gyssens
    • 2
  • Jan Paredaens
    • 3
  1. 1.Indiana UniversityUSA
  2. 2.Hasselt University & Transnational University of LimburgBelgium
  3. 3.University of AntwerpBelgium

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