Designing Information-Preserving Mapping Schemes for XML.

An XML-to-relational mapping scheme consists of a procedure for shredding documents into relational databases, a procedure for publishing databases back as documents, and a set of constraints the databases must satisfy. In previous work, we defined two notions of information preservation for mapping schemes: losslessness , which guarantees that any document can be reconstructed 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 validation are both undecidable. This leads to the question we study in this paper: how to design mapping 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 improvements over Edge++ and introduces constraints that are efficiently enforced in practice.