Bidirectional conversion between XML documents and relational databases

Relational databases have been used to support information storage for a long time. Maintenance and the natural growth of information systems imply the reuse of existing databases, but information is often not stored on the most convenient structure or on the desired platform; it then becomes necessary to export it into another system or to transform its structure. These tasks should be executed in a fast and safe way, with as much automation as possible. XML has been accepted as the neutral format for information representation. This is mainly due to two factors. On one hand, XML documents are purely textual files, structured and independent of any hardware or software platforms. On the other hand, more and more public domain tools are becoming available to help users transform XML documents. The paper focuses on the use XML as an interchange format between database management systems and presents an XML language, DBML, that allows the definition of the structure and content of a relational database. It also introduces a methodology to convert a database into a DBML document and two tools that allow transforming DBML documents into SQL and back. DBML and the two conversion functions (dbsql2dbml and dbml2dbsql) provided the basis to support the idea of designing a language to specify database transformations and developing a generator to automatically produce the transference processors; we finish the paper with the proposal of such a system.