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Unformatted text preview: Designing Information-Preserving Mapping Schemes for XML Denilson Barbosa Juliana Freire Alberto O. Mendelzon University of Calgary firstname.lastname@example.org University of Utah email@example.com University of Toronto firstname.lastname@example.org Abstract An XML-to-relational mapping scheme consists of a procedure for shredding documents into re- lational databases, a procedure for publishing databases back as documents, and a set of con- straints the databases must satisfy. In previ- ous work, we defined two notions of information preservation for mapping schemes: losslessness , which guarantees that any document can be re- constructed from its corresponding database; and validation , which requires every legal database to correspond to a valid document. We also described one information-preserving mapping scheme, called Edge ++ , and showed that, under reasonable assumptions, losslessness and valida- tion are both undecidable. This leads to the ques- tion we study in this paper: how to design map- ping schemes that are information-preserving. We propose to do it by starting with a scheme known to be information-preserving and applying to it equivalence-preserving transformations written in weakly recursive ILOG. We study an instance of this framework, the LILO algorithm, and show that it provides significant performance improve- ments over Edge ++ and introduces constraints that are eciently enforced in practice. 1 Introduction In order to use relational engines for managing XML data, we need a mapping scheme providing a procedure for shredding the documents into relational databases, a procedure for publishing the databases as docu- ments, and a set of constraints that those databases must satisfy. As with any other mapping strategy, it is important to study the information preservation properties of XML-to-relational mapping schemes in order to understand their suitability for a given ap- plication . Although there is a rich literature on mapping schemes [6, 14, 17, 22, 31, 23, 33], to date little attention has been given to their information- Most of this work was done while this author was a Ph.D. Student at the University of Toronto. Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the VLDB copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Very Large Data Base Endowment. To copy otherwise, or to republish, requires a fee and/or special permission from the Endowment. Proceedings of the 31st VLDB Conference, Trondheim, Norway, 2005 preservation capabilities. In previous work , we defined lossless mapping schemes as those that allow the reconstruction of the original documents, and val- idating mapping schemes as those in which all legal database instances correspond to a valid XML doc- ument. We argued that while losslessness is enough for applications involving only queries over the docu-...
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