Designing information-preserving mapping schemes for XML

An XML-to-relational mapping scheme consists of a procedure for shredding XML 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 discussed two notions of information preservation for mapping schemes: losslessness, which guarantees the complete reconstruction of a document from a database; and validation, which guarantees that every update to a database corresponding to a valid document results in a database corresponding to another valid document. Also, we described one information preserving mapping scheme, called Edge++, and showed that, under reasonable assumptions, lossless and validation are both undecidable. This leads to the question we study in this paper: how to design information-preserving mapping schemes. We propose to do it by starting with a scheme known to be information preserving (such as Edge++) and applying to it equivalence-preserving transformations written in weakly recursive ILOG. We study a particular incarnation of this framework, the LILO algorithm, and show that it provides signfii cant performance improvements over Edge++ and that the constraints it introduces are efficiently enforced in practice.