We present a system for publishing as XML data from mixed (relational+XML) proprietary storage, while supporting redundancy in storage for tuning purposes. The correspondence between public and proprietary schemas is given by a combination of LAV-and GAV-style views expressed in XQuery. XML and relational integrity constraints are also taken into consideration. Starting with client XQueries formulated against the public schema the system achieves the combined effect of rewriting-with-views, composition-with-views and query minimization under integrity constraints to obtain optimal reformulations against the proprietary schema. The paper focuses on the engineering and the experimental evaluation of the MARS system.
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