[XSL] How can I seek info in XML files and tranform it

Hello,
I need your help to choose the right tools to answer
the following question:
I have a server with lots of XML files stored in
folders. Each folder gathers the information
concerning one city. The files inside a folder all
contain the same kind of information(for example the
daily average temperature, the amount of rain ...) the
only difference between the different files inside a
folder is the date when the information was logged and
transfered to the server.
The goal is to have access to this information on the
web and to allow the visitor to choose if he wants to
consult information concerning 1 city at a given time
or to compare the information of different cities
between january and march....
I guess I'm going to use XSLT+SVG (and Java??) and a
XSLT processor such as Xalan. 
Does it seem a good solution to you? will XSLT and
java allow me to seek information in the folders in
order to answer the query?? or do I need to
investigate more carefully XQL??
According to you, what are the best solutions??

Thanks a lot for sharing your experience
ed

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