A study of a positive fragment of path queries: Expressiveness, normal form, and minimization

Y. Wu, D. Van Gucht, M. Gyssens, J. Paredaens

    Research output: Chapter in Book/Report/Conference proceedingConference contributionAcademicpeer-review


    We study the expressiveness of a positive fragment of path queries, denoted Path, on node-labeled trees documents. The expressiveness of Path is studied from two angles. First, we establish that Path 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 yields a normal form for Path queries. Using this normal form, we can decompose a Path query into sub-queries that can be expressed in a very small sub-fragment of Path for which efficient evaluation strategies are available. Second, we characterize the expressiveness of Path 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.
    Original languageEnglish
    Title of host publicationDataspace: The Final Frontier (26th British National Conference on Databases, BNCOD 26, Birmingham, UK, July 7-9, 2009. Proceedings)
    EditorsA.P. Sexton
    Place of PublicationBerlin
    ISBN (Print)978-3-642-02842-7
    Publication statusPublished - 2009

    Publication series

    NameLecture Notes in Computer Science
    ISSN (Print)0302-9743


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