We state and solve the query reformulation problem for XML publishing in a general setting that allows mixed (XML and relational) storage for the proprietary data and exploits redundancies (materialized views, indexes and caches) to enhance performance. The correspondence between published and proprietary schemas is specified by views in both directions, and the same algorithm performs rewritin...

Reformulation-based query answering is a query processing technique aiming at answering queries under constraints. It consists of reformulating the query based on the constraints, so that evaluating the reformulated query directly against the data (i.e., without considering any more the constraints) produces the correct answer set. In this paper, we consider optimizing reformulation-based query...

Whenever transformation of data is used to bridge the gap of different data formats, and a query is given in the destination format, query reformulation can speed up the transformation of data. We achieve this speed-up in transformation when only the required data segment, described by the computed reformulated query, is transformed. Whenever the required section of data is not too large, query...