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|Title: ||A study of a positive fragment of path queries: expressiveness, normal form, and minimization|
|Authors: ||WU, Yuqing|
VAN GUCHT, Dirk
|Issue Date: ||2009|
|Citation: ||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, 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.|
|Type: ||Proceedings Paper|
|Appears in Collections: ||Research publications|
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