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Finding a minimal tree pattern under neighborhood constraints

Published:13 June 2011Publication History

ABSTRACT

Tools that automatically generate queries are useful when schemas are hard to understand due to size or complexity. Usually, these tools find minimal tree patterns that contain a given set (or bag) of labels. The labels could be, for example, XML tags or relation names. The only restriction is that, in a tree pattern, adjacent labels must be among some specified pairs. A more expressive framework is developed here, where a schema is a mapping of each label to a collection of bags of labels. A tree pattern conforms to the schema if for all nodes v, the bag comprising the labels of the neighbors is contained in one of the bags to which the label of v is mapped. The problem at hand is to find a minimal tree pattern that conforms to the schema and contains a given bag of labels. This problem is NP-hard even when using the simplest conceivable language for describing schemas. In practice, however, the set of labels is small, so efficiency is realized by means of an algorithm that is fixed-parameter tractable (FPT). Two languages for specifying schemas are discussed. In the first, one expresses pairwise mutual exclusions between labels. Though W[1]-hardness (hence, unlikeliness of an FPT algorithm) is shown, an FPT algorithm is described for the case where the mutual exclusions form a circular-arc graph (e.g., disjoint cliques). The second language is that of regular expressions, and for that another FPT algorithm is described.

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    • Published in

      cover image ACM Conferences
      PODS '11: Proceedings of the thirtieth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
      June 2011
      332 pages
      ISBN:9781450306607
      DOI:10.1145/1989284

      Copyright © 2011 ACM

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      Association for Computing Machinery

      New York, NY, United States

      Publication History

      • Published: 13 June 2011

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