XML and Generating Data Stats

Hi,

I have a XML document that contains a series of rankings and scores of a series of areas within my district. The document isn't big, but I wanted to generate basic statistics from this document. Such as:

Min and Max value PER Numeric Column
Sum the data values from a row based on a certain range of columns.
And so forth...This will then be used to generate a range with differing colours on offer to indicate the banding of rank/score per area. Which in turn will then be incorporated into an SVG document where I can visually illustrate my data.

Now I have dabbled in XQuery and know how to use choose and FLWOR, but I'm not 100% sure on the use of variables within XML and how to use them to compile a footer table in HTML which will summarise the XML tables data...

Can anyone point me in the right direction and tell me if this is possible or not.

In short: I need to know how to use variables and edit/query them, and I need to know whether I can specify (serverside) certain values/criteria and then have the XSL document modifiy the data accordingly?

Ben