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 n then 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.
This research was supported by the German Research Society, Berlin-Brandenburg Graduate School in Distributed Information Systems (DFG grant no. GRK 316).
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Schlieder, T. (2002). Schema-Driven Evaluation of Approximate Tree-Pattern Queries. In: Jensen, C.S., et al. Advances in Database Technology — EDBT 2002. EDBT 2002. Lecture Notes in Computer Science, vol 2287. Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-45876-X_33
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DOI: https://doi.org/10.1007/3-540-45876-X_33
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