XML Middleware Articles
XML middleware or XML mapping is much like object-relational mapping. It usually involves mapping between XML and relational data, but can also include mapping between XML and object data.
Since XML is inherently important to XML middleware, be sure to look at the articles on XML.
Finally, in addition to the articles listed below, be sure to check out the database concepts and standards articles. Many of these database concepts apply to all forms of database management systems: relational (RDBMS), object (ODBMS), XML (XDBMS), and others as well as object-relational mapping and XML middleware or XML mapping products.