RE: [XQuery] 3.2 Order of nodes constructed in a path

Sorry to go off at rather a tangent, but I would love to have a rule
that limited the ability to create new nodes within a path expression.

It used to be true in XSLT that XPath expressions were side-effect free.
We now have this limited side-effect of creating new nodes, which is
possible even in XPath, because XPath expressions can call XSLT
functions that create new nodes. This greatly complicates the semantics
and makes life a lot more difficult for optimizers, without actually
providing any benefits to users. It just means we have to spend a lot of
time discussing pathological cases like the one you raise; we should
find a way to ban these.

It's tricky to define such a rule but I think it could be done, by
additions to the dynamic context. 

Michael Kay


> -----Original Message-----
> From: public-qt-comments-request@w3.org 
> [mailto:public-qt-comments-request@w3.org] On Behalf Of Sarah Wilkin
> Sent: 04 February 2004 21:14
> To: public-qt-comments@w3.org
> Subject: [XQuery] 3.2 Order of nodes constructed in a path
> 
> 
> 
> Currently the order of nodes constructed in a path is undefined for 
> many cases. For example:
> 
> let $source := <foo><a>1<a>2</a></a><a>3</a></foo>
> return $source/element bar { .//a/element b { text() } }
> 
> will return a variation of 
> <bar><b>1</b><b>3</b><b>2</b></bar> with the 
> "b" elements in an undefined, but stable, order. From 2.3.1 Document 
> Order: "The relative order of nodes in distinct trees is stable but 
> implementation-dependent, subject to the following constraint: If any 
> node in tree T1 is before any node in tree T2, then all nodes in tree 
> T1 are before all nodes in tree T2."
> 
> We feel this is unsatisfactory for embedded node creation; 
> the order of 
> created elements should be the same across implementations 
> (and runs on 
> the same implementation). One simple fix is to base the 
> document order 
> of new nodes in a path on their position. However, this brings up 
> problems where the position repeats. For example:
> 
> let $source :=
> <source>
> 	<foo><a>1<a>2</a></a><a>3</a></foo>
> 	<foo><a>4<a>5</a></a><a>6</a></foo>
> </source>
> return $source/element bar { .//a/element b { text() } }
> 
> Would end up with nodes 1 and 4 appearing before elements 2 and 5. We 
> would appreciate any input on this issue.
> 
> --Sarah
>

Received on Wednesday, 4 February 2004 16:52:52 UTC