XQuery middleware

[Ale]

Hi all!
I need to build a middleware for XQuery: I mean a software receiving a
std xquery and outputting the xquery result on "database.xml".
This middleware must use 7 or 8 different choosable XQuery
implementations... The XQuery received must be std for all
implementations. The middleware will parse the std XQuery in the
specific XQuery for the specific implementation, returning an error if
requested features isn't avaiable for the implementation choosed.

I've already built the editor and the DOM interface. My editor can read
DTD and load/view in a tree structure an XML database. Now I need to
integrate the first XQuery implementation and use it for execute my
XQuery on xml file.

I need first of all one simple implementation and and sample of use
about this implementation.

Thanks
Ale