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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Wu, Y., Van Gucht, D., Gyssens, M., Paredaens, J. (2009). A Study of a Positive Fragment of Path Queries: Expressiveness, Normal Form, and Minimization. In: Sexton, A.P. (eds) Dataspace: The Final Frontier. BNCOD 2009. Lecture Notes in Computer Science, vol 5588. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-02843-4_14
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DOI: https://doi.org/10.1007/978-3-642-02843-4_14
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