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Data warehouses evolution: trade-offs between quality and cost of query rewritings

Query rewriting with relaxed semantics has been proposed as a means of retaining the validity of a data warehouse (i.e., materialized queries) in a changing environment. Attributes in the query interface can be classified as essential or dispensable (if it cannot be retained) according to the query definer's preferences. Similarly, preferences for query extent can be specified, for example, to indicate whether a subset of the original result is acceptable or not. The paper discusses the trade-off between quality and cost of query rewriting.