get highest number

[Wolfgang]

> Or switch to a better XQuery processor. I find it hard to imagine why a
> product should take noticeably longer to evaluate max(//@id) than it takes
> to evaluate //@id.

If Gonzberg is using eXist (I remember other posts on the corresponding 
lists), I can explain the difference: evaluating //@id is entirely 
index-based (as John already suspected). Compared to this, max(//@id) 
requires access to the actual attribute nodes, which generates a lot 
more IO. Better index-support for aggregate functions would help here, 
but that's work in progress.

Wolfgang