[xquery-talk] outer for

[Michael Kay]

You're approaching this with a SQL mindset, and in my view that's not the
right place to start - we're dealing here with hierarchies rather than
tables.
 
I think it's often best to forget FLWOR expressions for this kind of thing
and go back to basic XPath, because XPath is more natural to the
hierarchical structure of XML. Keep FLWOR expressions for when you need to
do real joins using value-based relationships.
 
I'm having a little trouble working out what your query is intended to mean.
The predicate:
 
(($figure/title='Examples' or $section/title='Syntax) or
($figure/title='Examples' and $figure/image/@source='example.gif')))
 
has the form 
 
(A or B) or (A and C)
 
which is equivalent to
 
(A or B)
 
But let's imagine that the second test on $figure/title was looking for
'Examples2', I would then write the query as
 
 
book[author='Dan Suciu'][section/title='Syntax' or
section/figure/title='Examples' or section/figure[title='Examples2' and
image/@source='example.gif']]
 
No need for XQuery here - XPath 1.0 is quite sufficient.
 
Michael Kay
http://www.saxonica.com/


  _____  

From: talk-bounces at x-query.com [mailto:talk-bounces at x-query.com] On Behalf
Of Eric Robinson
Sent: 23 April 2009 17:50
To: talk at x-query.com
Subject: [xquery-talk] outer for



I was wondering if someone can help me with a xquery issue I am having.
 
What I am trying to do is create a web page that will allow a user to enter
information about what they are looking for in a xml document and return to
them the xml document if it matches their criteria. I thought I had it all
working till I hit an issue with missing repeatable complex types.
 
Example of xml and xquery that works.
 
<book>
  <title>Data on the web</title>
  <author>Dan Suciu</author>
  <section>
    <title>Introduction</title>
    <figure>
      <title>Traditional</title>
      <image source="csarch.gih"/>
    </figure>
    <figure>
      <title>Examples</title>
      <image source="example.gif"/>
    </figure>
  </section>
  <section>
    <title>Syntax</title>
  </section>
</book>
 
for $book in /book
for $section in $book/section
for $figure in $section/figure
where ($book/author='Dan Suciu' and (($figure/title='Examples' and
$section/title='Syntax) or ($figure/title='Examples' and
$figure/image/@source='example.gif')))
return $book
 
Since the xml matches the where at 
<figure>
      <title>Examples</title>
      <image source="example.gif"/>
</figure>
it returns me the enitre document like I want.
 
Example that breaks my xquery.
 
<book>
<title>Data on the web</title>
  <author>Dan Suciu</author>
  <section>
    <title>Introduction</title>
   </section>
  <section>
    <title>Syntax</title>
  </section>
</book>
 
for $book in /book
for $section in $book/section
for $figure in $section/figure
where ($book/author='Dan Suciu' and (($figure/title='Examples' or
$section/title='Syntax) or ($figure/title='Examples' and
$figure/image/@source='example.gif')))
return $book
 
This will always return nothing because there is no /book/section/figure in
the xml.
 
I believe once "outer for" is implemented I will be able to do 
 
for $book in /book
for $section in $book/section
outer for $figure in $section/figure
where ($book/author='Dan Suciu' and (($figure/title='Examples' or
$section/title='Syntax) or ($figure/title='Examples' and
$figure/image/@source='example.gif')))
return $book
 
 
Anyone have any ideas how I could get this to work?
 
 
 
 


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