31. A method comprising: a first database server running on one or more computers; said first database server creating a first database statement that defines a view based on first and second XML data; wherein the first XML data and the second XML data are based on a combination of any two from a group consisting of: (a) the first XML data is managed by said first database server and the second XML data is managed by a second database server, wherein the second database server is a different server than the first database server, (b) the first XML data is stored in a database based on a first data storage model and the second XML data is stored in the database based on a second data storage model, wherein the second data storage model is different than the first data storage model, (c) the first XML data conforms to a first version of an XML schema and the second XML data conforms to a second version of the XML schema, 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 first database server.
32. 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 31 .