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Title: A study of a positive fragment of path queries: expressiveness, normal form, and minimization
Authors: WU, Yuqing
Issue Date: 2009
Publisher: Springer
Source: Sexton, Alan P. (Ed.) Dataspace: The Final Frontier, 26th British National Conference on Databases, BNCOD 26, Birmingham, UK, July 7-9, 2009. Proceedings. p. 133-145.
Series/Report: Lecture Notes in Computer Science
Series/Report no.: 5588
Abstract: 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.
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ISBN: 978-3-642-02842-7
DOI: 10.1007/978-3-642-02843-4
Category: C1
Type: Proceedings Paper
Appears in Collections:Research publications

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