[xquery-talk] Find All Nodes Between Root Node and Descendant Nodes of Some Type

[Christian Grün]

Hi Eliot,

> In terms of processing optimization, is there any reason to prefer one
> formulation over the other (meaning, is it possible to predict how XPath
> processors will be able to optimize this type of expression)?

I like Ken's solution, but mostly because it's more concise. You will
never know what a specific implementation does, or what it will do in
a future version. It also depends on your data: If you have deep
document structures, the ancestor step may get more expensive. Just
create some gigabytes of test data and do some simple testing with the
processors of your choice.

However, your original query may be evaluated faster by some
processors if you move the path expression out of the predicate and
bind it to an additional variable:

  let $a1 := $doc/a
  let $a2 := $a1//a
  let $bsInA1 := $a1//b[not(ancestor::a = $a2)]

Cheers,
Christian