Schema-Driven Evaluation of Approximate Tree-Pattern Queries

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 nth entry. 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.

• Type: Conference
• Year: 2002
• Where: EDBT
• Authors: Torsten Schlieder
• Keywords: Boolean-connected Query Patterns, Cost-based Query Transformations, Database, EDBT 2002, Simple Query Language