A top-down approach to answering queries using views
The problem of answering queries using views is concerned with finding answers to a query using only answers to a set of views. In the context of data integration with LAV approach, this problem translates to finding maximally contained rewriting for a query using a set of views. When both query and...
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| Format: | Others |
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2008
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| Online Access: | http://spectrum.library.concordia.ca/975902/1/MR40949.pdf Mohajerin, Nima <http://spectrum.library.concordia.ca/view/creators/Mohajerin=3ANima=3A=3A.html> (2008) A top-down approach to answering queries using views. Masters thesis, Concordia University. |
| Summary: | The problem of answering queries using views is concerned with finding answers to a query using only answers to a set of views. In the context of data integration with LAV approach, this problem translates to finding maximally contained rewriting for a query using a set of views. When both query and views are in conjunctive form, rewritings generated by existing bottom-up algorithms in this context are generally expensive to evaluate. As a result, they often require costly post-processing to improve efficiency of computing the answer tuples. In this dissertation, we propose a top-down approach to the rewriting problem of conjunctive queries. We first present a graph-based analysis of the problem and identify conditions that must be satisfied to ensure maximal containment of rewriting. We then present TreeWise, a novel algorithm that uses our top-down approach to efficiently generate maximally contained rewritings that are generally less expensive to evaluate. Our experiments confirm that TreeWise generally produces better quality rewritings, with a performance comparable to the most efficient of previously proposed algorithms |
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