Redundancy free mapping from relations to XML

Given the fact that relational and object-relational databases are the most widely used technology for storing data and that XML is the standard format used in electronic data interchange, the process of converting relational data to XML documents is one that occurs frequently. The problem that we address in this paper is an important one related to this process. If we convert a relation to an XML document, under what circumstances is the XML document redundancy free? Drawing on some previous work by the authors that formally defined functional dependencies and redundancy in XML documents, we show that for a very general class of mappings from a relation to an XML document, the XML document is always redundancy free if and only if the relation is in Boyce-Codd normal form (BCNF).