Incorrect Intersect and Except Output?

[Wei, Alice J.]

Hi, Michael:

   Yes, I admit that I have not grasped this.
   According to what you said, are you implying that it is not even possible to even do an "outer-join" to produce the output from

  let $a := <a><b>1</b><b>2</b><b>3</b></a>,
      $b :=<c><b>What</b><b>2</b><b>3</b><b>4</b></c>
return
 <foo>{(($a/b union $b/b) except ($a/b except $b/b))}</foo>

to something like:

<foo>
<b>What</b>
<b>1</b>
<b>4</b>
</foo>?

Thanks a lot for your help.
======================================================
Alice Wei
MIS 2008
School of Library and Information Science
Indiana University Bloomington
http://x-query.com/mailman/listinfo/talk
________________________________________
From: Michael Kay [http://x-query.com/mailman/listinfo/talk]
Sent: Sunday, March 30, 2008 7:23 PM
To: Wei, Alice J.; 'Jonathan Robie'
Cc: http://x-query.com/mailman/listinfo/talk
Subject: RE:  Incorrect Intersect and Except Output?

No, you haven't grasped it.

let $a1 := <a/>, $a2 := <a/> return count(($a1, $a2))

returns 2. Thats because the two <a/> nodes are DIFFERENT - they have
different identity because they were created separately. The same logic
applies to intersect and except.

Michael Kay
http://www.saxonica.com/

> -----Original Message-----
> From: http://x-query.com/mailman/listinfo/talk
> [mailto:http://x-query.com/mailman/listinfo/talk] On Behalf Of Wei, Alice J.
> Sent: 31 March 2008 00:09
> To: Jonathan Robie
> Cc: http://x-query.com/mailman/listinfo/talk
> Subject: RE:  Incorrect Intersect and Except Output?
>
> Hi, Jonathan:
>
>   I think I understand what you mean by having different
> nodes in the both sets I have indicated. However, since
> <b>2</b><b>3</b> are co-shared between the two sets, this
> means that I have to go around by doing something like
>
> let $a := <a><b>1</b><b>2</b><b>3</b></a>, $b :=
> <c><b>What</b><b>2</b><b>3</b><b>4</b></c>
> return
> <foo>{(($a/b union $b/b) except ($a/b except $b/b))}</foo>
>
> Output:
>
> <foo>
> <b>What</b>
> <b>2</b>
> <b>3</b>
> <b>4</b>
> </foo>
>
> This is not exactly what I desired, but are you saying that I
> have to use union joins and combine it with other operators
> for the output? And, how can I get rid of the
> <b>2</b><b>3</b> and switch it with <b>1</b>?
>
> Thanks for your help.
>
> Alice
> ======================================================
> Alice Wei
> MIS 2008
> School of Library and Information Science Indiana University
> Bloomington http://x-query.com/mailman/listinfo/talk ________________________________________
> From: Jonathan Robie [http://x-query.com/mailman/listinfo/talk]
> Sent: Sunday, March 30, 2008 1:45 PM
> To: Wei, Alice J.
> Cc: http://x-query.com/mailman/listinfo/talk
> Subject: Re:  Incorrect Intersect and Except Output?
>
> Wei, Alice J. wrote:
> > let $a := <a><b>1</b><b>2</b><b>3</b></a>, $b :=
> > <c><b>What</b><b>2</b><b>3</b><b>4</b></c>,
> > return
> > <foo>{$a except $b}</foo>
> >
> > brings
> >
> > <foo>
> > <a>
> > <b>1</b>
> > <b>2</b>
> > <b>3</b>
> > </a>
> > </foo>
> >
>
> Except tests for node identity (you seem to expect it to test
> the node values). If none of the nodes in $a are also in $b,
> then $a except $b is the same as $a.
>
> > If I use $a intersect $b, it brings me an empty node <foo/> Isn't
> > intersect supposed to bring back what is contained in $b and $a?
> >
>
> Yes, but there are no nodes in $b that are also in $a, and vice versa.
>
> Jonathan
>
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