24. A volatile or non-volatile machine-readable storage medium storing one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 23 .
23. A method comprising: a database server running on one or more computers; said database server creating a first database statement that defines a view based on first and second XML data, wherein the first XML data is based on a first version of an XML schema and the second XML data is based on a second version of the XML schema, and wherein the second version of the XML schema describes a different data structure than the first version of the XML schema; wherein the first database statement includes a union, based on a UNION ALL operator, of a statement involving the first XML data and a statement involving the second XML data; and in response to receiving a second database statement that involves the view, executing the first database statement by said database server.