define views using xquery

I'd like to use XQuery as a view definition language to define XML views. but I find that it is difficult to use it as the view definition language, because a simple view definition have to lead to a complex XQuery. even more, it may be inefficient. comparing with view definition in SQL, it is inconvenient.

can anybody give me advices of how to utilize XQuery to define XML view more efficiently?
and how will the XQuery WD support the view facility.

Best regards,
Chen