[Exist-open] multiple sort keys

[Ron V. d. B. <ron...@ho...>]

Hello all,

Does anyone know whether it is possible at all to define multiple sort keys 
for queries with the XMLDB logicsheet or the XMLDB Transformer? Postponing 
sorting to XSLT processing is no option, since the total result set should 
be ordered before presenting to the user.

The closest I can get is by defining a "sort-by" XPath expression 
identifying a parent element that  happens to contain all child elements I 
would like to use to control sorting. In my case, the relevant part of the 
structure is this:

<letHeading>
  <author>...</author>
  <addressee>...</addressee>
  <placeLet>...</placeLet>
  <dateLet>...</dateLet>
</letHeading>

When specifying <xmldb:for-each select="..." sort-by="letHeading">, this 
returns a list of results ordered first along their author, then addressee, 
then placeLet, and finally dateLet information (since the XPath expression 
evaluates to a concatenation of the string values of all child elements). 
Yet, this is only a superficial solution, since such an expression allows no 
other ordering of sort keys than that contained in the source documents. 
I've tried to change this order by specifying the sort expression as eg. 
"concat(letHeading/placeLet, letHeading/dateLet, letHeading/author, 
letHeading/addressee)"; yet this returns following error:

org.apache.cocoon.ProcessingException: Failed to execute pipeline.: 
java.lang.RuntimeException: java.lang.RuntimeException: function not found

Nesting of <xmldb:for-each> elements with different "sort-by" expressions 
does not seem to work either. Does anyone have a working solution or perhaps 
a clever XPath workaround for the definition of secondary sort keys?

Any help or comments are greatly appreciated!

Ron

--
Ron Van den Branden
Project Officer
Centrum voor Teksteditie en Bronnenstudie (CTB)
Centre for Scholarly Editing and Document Studies
Koninklijke Academie voor Nederlandse Taal- en Letterkunde
Koningstraat 18 / b-9000 Gent / Belgium
http://www.kantl.be/ctb/staff/ron.htm

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