[anamax]

Is there some reason why you can't save the DOM or other datastructures that you help you query/manipulate the XML?

A database isn't a set of flat-file CSVs even though that's all that is actually needed to do everything that people do with databases (albeit one operation at a time). (The data may be normalized but the datastructures aren't necessarily.) Instead, a database is data together with some data structures (and relevant code) that are maintained to speed up operations on said data.

Why can't one persist auxillary datastructures for XML, including (but not limited to) the DOM?