[xquery-talk] get highest number

Florent Georges lists at fgeorges.org
Sat May 17 15:33:30 PDT 2008

Andrew Welch wrote:

  Hi Andrew

> >> > 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.

> > Thanks for the info. Obvious, when you think about it.

> Not to me - can someone explain this a little more for me...

  //@id could return something that "stands for" the actual nodes,
using an index and being quite fast.  But max(//@id) has to dereference
that "something" and to access to the nodes themselves to compare their

  That's not XQuery, that's expectations about how an implementation
can introduce difference between those two expressions.  For example I
would expect to see that difference in an XML database but not in a
standalone processor as Saxon.

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