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)


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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  1. 1.
    Al-Khalifa, S., Jagadish, H.V., Patel, J.M., Wu, Y., Koudas, N., Srivastava, D.: Structural joins: A primitive for efficient XML query pattern matching. In: ICDE (2002)Google Scholar
  2. 2.
    Amer-Yahia, S., Cho, S., Lakshmanan, L.V.S., Srivastava, D.: Tree pattern query minimization. VLDB J. 11(4), 315–331 (2002)CrossRefMATHGoogle Scholar
  3. 3.
    Benedikt, M., Fan, W., Kuper, G.M.: Structural properties of XPath fragments. Theor. Comput. Sci. 336(1), 3–31 (2005)MathSciNetCrossRefMATHGoogle Scholar
  4. 4.
    Brenes, S., Wu, Y., Gucht, D.V., Cruz, P.S.: Trie indexes for efficient XML query evaluation. In: WebDB (2008)Google Scholar
  5. 5.
    Chamberlin, D., et al.: XQuery 1.0: An XML query language, W3C (2003)Google Scholar
  6. 6.
    Clark, J., DeRose, S.: XML path language (XPath) version 1.0, http://www.w3.org/TR/XPATH
  7. 7.
    Fletcher, G.H.L., Van Gucht, D., Wu, Y., Gyssens, M., Brenes, S., Paredaens, J.: A methodology for coupling fragments of XPath with structural indexes for XML documents. In: Arenas, M., Schwartzbach, M.I. (eds.) DBPL 2007. LNCS, vol. 4797, pp. 48–65. Springer, Heidelberg (2007)CrossRefGoogle Scholar
  8. 8.
    Gottlob, G., Koch, C., Pichler, R.: Efficient Algorithms for Processing XPath Queries. ACM Trans. Database Syst. 30(2), 444–491 (2005)CrossRefGoogle Scholar
  9. 9.
    Götz, M., Koch, C., Martens, W.: Efficient algorithms for the tree homeomorphism problem. In: Arenas, M., Schwartzbach, M.I. (eds.) DBPL 2007. LNCS, vol. 4797, pp. 17–31. Springer, Heidelberg (2007)CrossRefGoogle Scholar
  10. 10.
    Gyssens, M., Paredaens, J., Gucht, D.V., Fletcher, G.H.L.: Structural characterizations of the semantics of XPath as navigation tool on a document. In: PODS (2006)Google Scholar
  11. 11.
    Kaushik, R., Shenoy, P., Bohannon, P., Gudes, E.: Exploiting local similarity for indexing paths in graph-structured data. In: ICDE (2002)Google Scholar
  12. 12.
    Koch, C.: Processing queries on tree-structured data efficiently. In: PODS (2006)Google Scholar
  13. 13.
    Marx, M., de Rijke, M.: Semantic characterizations of navigational XPath. SIGMOD Record 34(2), 41–46 (2005)CrossRefGoogle Scholar
  14. 14.
    Miklau, G., Suciu, D.: Containment and equivalence for a fragment of XPath. J. ACM 51(1), 2–45 (2004)MathSciNetCrossRefMATHGoogle Scholar
  15. 15.
    Paparizos, S., Patel, J.M., Jagadish, H.V.: SIGOPT: Using schema to optimize XML query processing. In: ICDE (2007)Google Scholar

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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