Schema-Driven Evaluation of Approximate Tree-Pattern Queries

  • Authors:

  • Torsten Schlieder

  • Affiliations:

  • -

  • Venue:
  • EDBT '02 Proceedings of the 8th International Conference on Extending Database Technology: Advances in Database Technology
  • Year:
  • 2002

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Abstract

We present a simple query language for XML, which supports hierarchical, Boolean-connected query patterns. The interpretation of a query is founded on cost-based query transformations: The total cost of a sequence of transformations measures the similarity between the query and the data and is used to rank the results. We introduce two polynomial-time algorithms that efficiently find the best n answers to the query: The first algorithm finds all approximate results, sorts them by increasing cost, and prunes the result list after the nthen try. The second algorithm uses a structural summary -the schema- of the database to estimate the best k transformed queries, which in turn are executed against the database. We compare both approaches and show that the schema-based evaluation outperforms the pruning approach for small values of n. The pruning strategy is the better choice if n is close to the total number of approximate results for the query.