XML import and export modules to connect XML applications
Ask your database manufacturer: they all provide XML import and export modules to connect XML applications with databases.
In some trivial cases there will be a 1:1 match between field names in the database table and element type names in the XML Schema or DTD, but in most cases some programming will be required to establish the desired match. This can usually be stored as a procedure so that subsequent uses are simply commands or calls with the relevant parameters.
Alternatively, most database systems now provide an XML dump format that lets you export a table as-is, for example by surrounding the field values with tags called after the fieldnames.
In less trivial, but still simple, cases, you could export by writing a report routine that formats the output as an XML document by adding the relevant tags as literals before and after each data value; and you could import by writing an XSLT transformation that formatted the XML data as a load file in your database’s preferred format.