Hi Dilip,



At 02:28 PM 11/1/2004, you wrote:
Hi,



I'm fairly new to XML and I'm trying to modify my query so that it fetches 
the preceding sibling to

the originally requested node if the originally requested node does not exist.

Sounds fine, up to the point where you say you want the preceding sibling 
of a node that doesn't exist ... XSLT isn't smart enough to know where in 
the input a node would be if it existed.



For example:

if my original query was something like

 child::data[attribute::id = 
'archive'][@id='archive']/child::timestamp[attribute::time = '1099119599']



and if the node with that particular timestamp is not present in the XML 
document I'd like to modify my query

in such a way that it fetches the node that has a timestamp < 1099119599.



I understand if I change my query to

child::data[attribute::id = 
'archive'][@id='archive']/child::timestamp[attribute::time < '1099119599']

then all the nodes with timestamp < 1099119599 get returned

That's correct.



Yet if your nodes are already ordered by time (which assumption is built 
into your question), you can get the last of this set in document order by 
grouping the set and using a predicate on the group. The last() function, 
which returns the size of the group, is designed for use in exactly this 
kind of situation. Using the query you've constructed (while removing that 
second, redundant predicate and changing '<' to '<=' in case that exact 
timestamp exists after all), that would be



(child::data[attribute::id = 'archive']/child::timestamp[attribute::time 
&lt;= '1099119599'])[position() = last()]



or abbreviating this:



(data[@id = 'archive'][@id='archive']/timestamp[@time &lt;= 
'1099119599'])[last()]



Cheers,
Wendell


======================================================================
Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
Mulberry Technologies, Inc.                http://www.mulberrytech.com
17 West Jefferson Street                    Direct Phone: 301/315-9635
Suite 207                                          Phone: 301/315-9631
Rockville, MD  20850                                 Fax: 301/315-8285
----------------------------------------------------------------------
  Mulberry Technologies: A Consultancy Specializing in SGML and XML
======================================================================