Developing query rewriting techniques to resolve XML data integration Problems based on a static analysis.

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Fusion is a known technique for eliminating unnecessary intermediate results that are created but then consumed during computation. Being useful for query optimization for many query languages such as SQL, fusion remains as a challenge for XQuery optimization. This is because XQuery has more complicated semantics ; it is context sensitive and requires preservation of document order. In this research, we proposed, as far as we are aware, the first XQuery fusion that can deal with both the document order and the context of XQuery expressions. More specifically, we carefully designed a context representation of XQuery expressions based on the Dewey order encoding, developed a context-preserving XQuery fusion for ordered trees by static emulation of the XML store, and proved that our fusion is correct. Our XQuery fusion has been implemented and successfully applied to the multi-step schema mapping, in which fusion is particularly necessary for reducing execution cost of redundant node creations.