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