[xquery-talk] Question on expected XQuery return per standards

Ronald Bourret rpbourret at rpbourret.com
Fri Mar 27 12:06:54 PST 2009

Hmmm. I would have thought that, in each case, only p2 is returned.

According to the spec, "For each item in the input sequence, the 
predicate expression is evaluated using an inner focus, defined as 
follows: The context item is the item currently being tested against the 
predicate. The context size is the number of items in the input 
sequence. The context position is the position of the context item 
within the input sequence."

In each case, the input sequence is the result of $xml//p, which is a 
sequence of four p elements. Since the position is the position within 
this sequence, only p2 is in the second position.

But I'm sure I could be wrong...

-- Ron

David Sewell wrote:
> Over on another list there has been a discussion of unexpected results
> from an XQuery like the following. The issues are how the parser
> interprets, in particular, the abbreviated syntax '//' and '[N]' as an
> equivalent to '[position() eq N]'.
> My belief is that the standard requires that two nodes (p2, p4) should
> be returned for result sets 1-4 below, because the interpretation of the
> XPath should in each case be identical. Set 5, on the other hand, should
> return only p2.
> We're seeing different behavior from a couple of XML parsers. Anyone
> care to read from the stone tablets on this one?
> (: begin query :)
> let $xml :=
>   <root>
>     <div>
>       <p>p1</p>
>       <p>p2</p>
>     </div>
>     <div>
>       <p>p3</p>
>       <p>p4</p>
>     </div>
>   </root>
> return (
>   <set1>{ $xml/descendant-or-self::node()/p[position() eq 2] }</set1>,
>   <set2>{ $xml//p[position() eq 2] }</set2>,
>   <set3>{ $xml/descendant-or-self::node()/p[2] }</set3>,
>   <set4>{ $xml//p[2] }</set4>,
>   <set5>{ $xml/descendant::p[2] }</set5>
> )
> (: end query :)
> David S.
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