A generic load/extract utility for data transfer between XML documents and relational databases

XML is rapidly gaining momentum in e-commerce and Internet-based information exchange, where its simplicity and custom-defined tags make it usable as a semantics-preserving data exchange format. However, to realize this potential it is necessary to be able to extract structured data from XML documents and store it in a database, as well as to generate XML documents from data extracted from a database. Although many DBMS vendors are scrambling to extend their products to handle XML, there is a need for a lightweight, DBMS- and platform-independent load/extract utility as well. In this paper, we describe such a utility that solves the following problems: (1) loading data from XML documents into relational tables with a known schema, (2) creating XML documents according to a known document type definition (DTD) from data extracted from a database, (3) generating relational schemas from XML DTDs for on-the-fly storage of XML documents, and (4) generating XML DTDs from relational schemas for on-the-fly extraction of relational data. We introduce a language to describe a mapping between an existing XML DTD and an existing relational schema and discuss some of the interesting issues arising from such a mapping.