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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.

Keywords

Normal Form Query Language Query Evaluation Conjunctive Query Label Tree 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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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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