Effective Schema Conversions between XML and Relational Models

As Extensible Markup Language (XML) is emerging as the data format of the Internet era, there is an increasing need to efficiently store and query XML data. At the same time, as requirements change, we expect a substantial amount of conventional relational data to be converted or published as XML data. One path to accommodate these changes is to transform XML data into relational format (and vice versa) to use the mature relational database technology. In this paper, we present three semantics-based schema transformation algorithms towards this goal: 1) CPI converts an XML schema to a relational schema while preserving semantic constraints of the original XML schema, 2) NeT derives a nested structured XML schema from a flat relational schema by repeatedly applying the nest operator so that the resulting XML schema becomes hierarchical, and 3) CoT takes a relational schema as input, where multiple tables are interconnected through inclusion dependencies and generates an equivalent XML schema as output.