Define no-overlaps constraint based on two integers (range index?)

[Michael Ludwig]

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