[xquery-talk] Define no-overlaps constraint based on two integers(range index?)

[Michael Kay]

I think you'll be extraordinarily lucky to find a product that does this for
you automatically, and efficiently. However it's easy enough to check the
condition by hand, with reasonable efficiency so long as you can access
everything in the collection efficiently:

let $ranges :=
  for $doc in collection(...) return
    <range start="{$doc/doc/@start}" end="{$doc/doc/@end}"/>
let $sortedRanges :=
  <ranges>{
    for $range in $ranges order by xs:integer($range/@start) return $range
  }</ranges>
let $valid := empty($sortedRanges/range[xs:integer(@start) le
xs:integer(preceding-sibling::range/@end)])
return $valid
  
If scanning the collection is too expensive, then you can maintain a
document "by hand" that contains the ranges redundantly.

Regards,

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

> -----Original Message-----
> From: talk-bounces at x-query.com 
> [mailto:talk-bounces at x-query.com] On Behalf Of Michael Ludwig
> Sent: 03 June 2009 10:18
> To: talk at x-query.com
> Subject: [xquery-talk] Define no-overlaps constraint based on 
> two integers(range index?)
> 
> I have a lot of documents in an XML database (Oracle Berkeley 
> DB XML), which look like this:
> 
>    <doc start="100123" end="100456">Huhu</doc>
> 
> Do you see any possibility to define an index on a database (on *any*
> database) such that no two documents with an overlapping 
> period from @start to @end can exist? Both @start and @end 
> are integers. Given the above document, no document may start 
> or end in the interval between
> 100123 and 100456.
> 
> I know this problem is rather general, unrelated to XQuery, 
> and not even specific to DBXML, of which I've already 
> consulted the forum:
> 
> http://forums.oracle.com/forums/message.jspa?messageID=3482507
> 
> I also know this problem could have an XQuery solution coded 
> at the application level, based on equality indices on @start 
> and @end.
> 
> Pointers to better places to ask this are as welcome as hints 
> to a solution. I'm not sure what this kind of index is 
> called; I thought of "contiguity index", or "range index", or 
> "interval index", but can't find much in Google. Does anyone know?
> 
> Michael Ludwig
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